Complex Patterns of Inheritance

Transcription

1 CHAPTER 6 Complex Patterns of Inheritance Specific Expectations In this chapter, you will learn how to... D1.1 analyze, on the basis of research, some of the social and ethical implications of research in genetics and genomics (6.3) D1.2 evaluate, on the basis of research, the importance of some recent contributions to the knowledge, techniques, and technologies related to genetic processes (6.3) D 2.1 use appropriate terminology related to genetic processes (6.1, 6.2, 6.3) D2.3 use the Punnett square method to solve basic genetics problems involving monohybrid crosses, incomplete dominance, codominance, dihybrid crosses, and sex-linked genes (6.1, 6.2) D3.3 explain the concepts of genotype, phenotype, dominance, incomplete dominance, codominance, recessiveness, and sex linkage according to Mendelian laws of inheritance (6.1, 6.2) D3.4 describe some genetic disorders caused by chromosomal abnormalities or other genetic mutations in terms of chromosomes affected, physical effects, and treatments (6.1, 6.2) The inherited traits of an individual are the result of a complex array of genetic interactions. As genetics research continues to advance, we have a better understanding of these complexities. A significant advancement is the Human Genome Project. In 2003, a team of over 2000 researchers, working in laboratory groups around the world, completed the Human Genome Project. For this project, numerous images like the one shown here were analyzed. This photo shows the products of chemical reactions that are used to identify the nucleotide sequence of a piece of DNA. Scientists used these to determine, base by base, the DNA sequence of the human genome. Other goals of the Human Genome Project included identifying all of the human genes and making them available for study. Because such scientific goals have consequences for society, there are also groups of researchers that explore and monitor the ethical and social impacts of these scientific achievements. 240 MHR Unit 2 Genetic Processes

2 Launch Activity Assembling a Mini-Genome The 46 chromosomes that make up our genome contain over base pairs. Each chemical reaction that is used to determine the sequence of DNA can only provide the sequence of a few hundred bases at a time. Therefore, to determine the DNA sequence of the human genome, scientists all over the world worked together to analyze millions of DNA sequencing reactions. They then assembled the DNA sequence of the human genome by piecing together the much smaller fragments of sequences. In this activity, you will model how scientists did this. output ultraviolet light gel lanes gel detector computer TATAAAAC TTTTAAAA T T TT T TT T TT TT T T TT T 140 A GC T AG ACCCAG ACC C AG C C AAAG CCCAA G G CAC A GG CAC AA GGGACCA The products of a DNA sequencing reaction are modified so they are visible under ultraviolet light. They are then separated in each lane of a gel-like material. The information in each lane is sent to a computer, which provides output in the form of a printout of the sequence of bases in a piece of DNA. Recall that nucleotides are often identified by their bases. For these data, red bands represent thymines, green bands represent adenines, blue bands represent cytosines, and black bands represent guanines. Materials paper DNA fragments tape Procedure 1. Obtain the sequence of DNA that you are to work with from your teacher. 2. With your classmates, construct one continuous segment of sequenced DNA from your individual fragments by matching overlapping sections and taping them into place. Questions 1. How did you decide how to match and link the fragments together? 2. How important was it to collaborate and discuss your results with other class members in order to obtain the full sequence? 3. How important do you think it was for scientists to develop a systematic and organized approach to sequencing the human genome? How do you think computers played a role? Chapter 6 Complex Patterns of Inheritance MHR 241

3 SECTION 6.1 Beyond Mendel s Observations of Inheritance Key Terms incomplete dominance codominance heterozygous advantage continuous variation polygenic trait incomplete dominance a condition in which neither allele for a gene completely conceals the presence of the other; it results in intermediate expression of a trait Figure 6.1 When red (C R C R ) flowers and white (C W C W ) flowers of the snapdragon are crossed, the resulting offspring have an intermediate phenotype, pink flowers (C R C W ). In the F 2 generation, all three phenotypes are observed. Much of today s genetics research uses sophisticated technologies to study cellular processes at the level of individual molecules and atoms. In addition, international research collaborations and multi-million-dollar budgets are now common. Think of what a stark contrast this is to Mendel s experiments. It is astounding that Mendel s basic and, at times, simple observations led him to infer patterns of inheritance that still form the basis of our current understanding of heredity. As more sophisticated experimental technologies became available, scientists realized that patterns of inheritance are more complicated than what Mendel proposed. Some patterns result in phenotypes that are between dominant and recessive phenotypes. Other patterns result in phenotypes that are created when both alleles for a trait are equally expressed. Incomplete Dominance Incomplete dominance describes a condition in which neither of the two alleles for the same gene can completely conceal the presence of the other. As a result, a heterozygote exhibits a phenotype that is somewhere between a dominant phenotype and a recessive phenotype. One example is the flower colour of snapdragons (Antirrhinum majus). As you can see in Figure 6.1, a cross between a true-breeding red-flowered plant and a true-breeding white-flowered plant produces offspring with pink flowers in the F 1 generation. If the F 1 plants are allowed to self-fertilize, the F 2 generation will include offspring with all three phenotypes red, pink, and white. The Punnett square in Figure 6.1 predicts that all three phenotypes will be observed in the F 2 generation in a ratio of 1:2:1 (red:pink:white), which is what is observed experimentally. In true Mendelian inheritance, we would have predicted a phenotypic ratio of 3:1. Nevertheless, the alleles for flower colour do segregate according to Mendel s law of independent assortment. When representing incomplete dominance, upper-case and lower-case letters are not usually used to represent the alleles, since neither allele is dominant over the other. One way to represent incomplete dominance is by using superscripts. In the example of snapdragon flower colour, both alleles affect the colour of the flower, C. The two alleles are represented as superscripts, R for red (C R ), and W for white (C W ). Lower-case letters are only used to represent a recessive allele. P generation F 1 generation F 2 generation red C R C R gametes C R self-fertilization of F 1 offspring C R C W C R C W C R C R C R C W C R C W C W C W C W pink C R C W C W C W white 242 MHR Unit 2 Genetic Processes

4 Incomplete Dominance and Human Disease There are many examples of genetic disorders in humans that exhibit incomplete dominance. For example, there is a genetic disorder, called familial hypercholesterolemia, that prevents tissues from removing low-density lipoproteins (LDL) from the blood and causes very high levels of cholesterol in the bloodstream. In the majority of cases, the disorder is due to a mutation in the LDLR gene. LDL particles transport molecules like cholesterol throughout the body. The mutated version of the LDLR gene no longer produces a protein that interacts with LDL particles and removes them from the bloodstream. This disorder has an autosomal dominant inheritance pattern. So, an individual only requires one allele of the mutated form of the gene to show symptoms of the disorder. However, if the allele for the normal form of the gene is present, symptoms of the disease will not be as severe. People who are homozygous dominant for the trait have six times the normal amount of LDL in their blood and may have a heart attack by the age of 2. Heterozygotes have about twice as much cholesterol in their blood and may have a heart attack by the age of 35. Scientists are now finding that identifying the patterns of inheritance for many traits is not as straightforward as first thought. Today s more accurate techniques are showing that, in some cases, what had been identified as a dominant inheritance pattern may actually be incomplete dominance. As a result, an individual who is heterozygous for a trait is not exactly the same as an individual who is homozygous dominant for the trait. Codominance Codominance is a situation in which both alleles are fully expressed. A roan animal is an excellent, visible example of codominance. A roan animal is a heterozygote in which both the base colour and white are fully expressed. If you look closely at the individual hairs on a roan animal, such as the cow in Figure 6.2, you will see a mixture of red hairs and white hairs. One allele is expressed in the white hairs, and the other allele is expressed in the red hairs. codominance the condition in which both alleles for a trait are equally expressed in a heterozygote; both alleles are dominant Figure 6.2 A roan cow is the product of a mating between a red cow and a white cow. The red and white hairs may be present in patches, as shown here, or be completely intermingled. Chapter 6 Complex Patterns of Inheritance MHR 243

5 heterozygous advantage a survival benefit for individuals who inherit two different alleles for the same trait Figure 6.3 Normal red blood cells are flat and disk-shaped. Sickle-shaped cells are elongated and C shaped. Sickle Cell Anemia Sickle cell anemia is one of the most thoroughly studied genetic disorders. Although it is often described as being the result of autosomal recessive inheritance, it is actually an example of codominance. Sickle cell anemia is caused by a specific form of the gene that directs the synthesis of hemoglobin. Hemoglobin carries oxygen in the blood. The hemoglobin molecule that is made in individuals with the sickle cell allele leads to a C-shaped (or sickled) red blood cell. These misshaped red blood cells, like the one shown in Figure 6.3, do not transport oxygen effectively because they cannot pass through small blood vessels. This leads to blockages and tissue damage. The allele for normal hemoglobin is represented as Hb A, and the allele for sickle cell hemoglobin is represented as Hb S. As shown in Figure 6.4, individuals who are homozygous (Hb S Hb S ) have sickle cell anemia. Individuals who are heterozygous (Hb A Hb S ) have some normal and some sickled red blood cells. These individuals are said to have the sickle cell trait, but they rarely experience any symptoms. In fact, having the sickle cell trait can be an advantage, because these heterozygotes are more resistant to malaria. Malaria is a life-threatening disease caused by a parasite that is transmitted to humans through mosquito bites. The parasite infects the liver and eventually the red blood cells. The sickling of red blood cells is thought to prevent the parasites from infecting the cells. Resistance to malaria is very beneficial in certain parts of Africa, where deadly epidemics can occur. The sickle cell trait is an example of the principle of heterozygous advantage, which describes a situation in which heterozygous individuals have an advantage over both homozygous dominant and homozygous recessive individuals. Hb A Hb S Hb A Hb A Hb A Hb A Hb S sickle cell trait Hb A Hb A Hb A Hb S Hb A Hb S Hb S Hb S sickle cell trait Hb S Hb A Hb S Hb S Hb S normal sickle cell trait sickle cell trait sickle cell anemia Figure 6.4 When a man and a woman are both heterozygous for the sickle cell gene, there is a one in four chance that they will have a child with sickle cell anemia. Learning Check 1. Distinguish between incomplete dominance and codominance. 2. Why do geneticists use notations like C W and C R to describe incomplete or codominant alleles instead of using W and w or R and r? 3. A plant that produces white flowers is crossed with a plant that produces purple flowers. Describe the phenotype of the offspring if the inheritance pattern for flower colour is a. incomplete dominance b. codominance 4. The frequency of the appearance of the sickle cell allele in human populations is much higher in Africa than in most other areas of the world. What has been proposed to explain this observation? 5. Provide two pieces of evidence that support the idea that some inheritance patterns are more complex than those originally proposed by Mendel. 6. Scientists first thought that sickle cell anemia was inherited as an autosomal recessive allele. What led them to identify the true inheritance pattern of the disease? 244 MHR Unit 2 Genetic Processes

6 Multiple Alleles The traits you have studied so far have all been controlled by one gene with two alleles, such as the flower colour in pea plants. Many traits in humans and other species are the result of the interaction of more than two alleles for one gene. A gene with more than two alleles is said to have multiple alleles. As you know, any individual has only two alleles for each gene one allele on each homologous chromosome. However, many different alleles for a gene can exist within the population as a whole. Human Blood Groups Do you know what blood type you are? In humans, a single gene determines a person s ABO blood type. This gene determines what type of an antigen protein, if any, is attached to the cell membrane of red blood cells. An antigen protein is a molecule that stimulates the body s immune system. The gene is designated I, and it has three common alleles: I A, I B, and i. As shown in Figure 6.5, the different combinations of the three alleles produce four different phenotypes, which are commonly called blood types A (I A I A homozygotes or I A i heterozygotes), B (I B I B homozygotes or I B i heterozygotes), AB (I A I B heterozygotes), and O (ii homozygotes). The I A allele is responsible for the presence of an A antigen on the red blood cells. The I B allele is responsible for the presence of the B antigen, and the i allele results in no antigen. Of the three alleles that determine blood type, one (i ) is recessive to the other two, and the other two (I A and I B ) are codominant. Rabbit Coat Colour Another example of multiple alleles involves coat colour in rabbits, as shown in Figure 6.6. The gene that controls coat colour in rabbits has four alleles: agouti (C ), chinchilla (c ch ), Himalayan (c h ), and albino (c). In that order, each allele is dominant to all the alleles that follow. The order of dominance sequence can be written as C > c ch > c h > c, where the symbol > means is dominant to. Possible alleles from male l A or l B or i Possible alleles from female l A or l B or i l A l A l A l B l A i l A l B l B l B l B i l A i l B i ii blood types A AB B O Figure 6.5 Different combinations of the three I alleles result in four different blood types: type A, type B, type AB, and type O. agouti Himalayan chinchilla albino Figure 6.6 Rabbits have multiple alleles for coat colour, with four possible phenotypes. Predict the possible genotypes for each rabbit. Chapter 6 Complex Patterns of Inheritance MHR 245

7 Clover Leaf Patterns The pattern on the leaves of the clover plant is also controlled by multiple alleles. While a single gene is responsible for clover leaf pattern, there are seven different alleles for the pattern. Varying combinations of these result in 22 different patterns that can be expressed in clover leaves. Patterns for the seven homozygous combinations of alleles are shown in Figure 6.7. Figure 6.7 There are seven different alleles for clover leaf pattern. v/v v l /v l v h /v h v f /v f v ba /v ba v b /v b v by /v by Sample Problem Using a Punnett Square to Analyze Inheritance of Multiple Alleles Problem If a man has type O blood and a woman has type B blood, what possible blood types could their children have? If this couple has six children, all with type B blood, what could you infer about the woman s genotype? What Is Required? You are asked to determine all possible blood types of the children and the possible genotype of the mother based on all the children having type B blood. What Is Given? The man has blood type O, the woman has blood type B. Plan Your Strategy Determine the possible genotypes of the man and the woman. Make Punnett squares for all the possible combinations of genotypes. Act on Your Strategy Since the man has blood type O, his genotype must be ii. The woman has blood type B, so her genotype could be either I B I B or I B i. father mother I B I B i I B i I B i i I B i I B i father mother I B i I B i ii i I B i ii i List all the possible genotypes and phenotypes of the children. What could be the mother s genotype based on the children being type B? The children could have genotype I B i, resulting in type B blood, or genotype ii, resulting in type O blood. The mother`s genotype is most likely I B I B. Check Your Solution The only genotype that produces type O blood is ii. To have type B blood, the woman must have at least one I B allele. Her second allele could be either I B or i. Since all of the children had to receive an i allele from their father, they must have inherited an I B allele from their mother. Since all of the children have type B blood, the mother is most likely I B I B. 246 MHR Unit 2 Genetic Processes

8 Practice Problems 1. If a man has type AB blood and a woman has type A blood, what possible blood types could their children have? 2. A baby has blood type AB. If the baby s mother has blood type B, what blood type(s) could the father have? 3. A couple just brought home their new baby from the hospital. They begin to suspect that the hospital switched babies, and the baby they brought home is not theirs. They check the hospital records, and find that the man s blood type is B, the woman s blood type is AB, and the baby s blood type is O. Explain why the parents are or are not justified in their concern about this baby. 4. Four children have the following blood types: A, B, AB, and O. Could these children have the same two biological parents? Explain. 5. Some of the offspring of a chinchilla rabbit and a Himalayan rabbit are albino. What are the genotypes of the parents? 6. A chinchilla rabbit with genotype c ch c h is crossed with a Himalayan rabbit with genotype c h c. What is the expected ratio of phenotypes among the offspring of this cross? 7. Could a mating between a chinchilla rabbit and an albino rabbit produce a Himalayan rabbit? Explain your reasoning. Your answer should include reference to the genotypes and phenotypes of the parents and the offspring. 8. In one family, all three siblings have type B blood. a. Use Punnett squares to show how two different sets of parent genotypes could produce this result. b. Which of the two sets of potential parents in your answer to (a) is more likely to be the parents of these siblings? Explain why. 9. In dogs, coat colour is determined by the interaction between three alleles. The allele A S produces a dark coloured dog, a y produces a sandy coloured dog, and a t produces a spotted dog. The order of dominance is A S > a y > a t. Determine the following from the pedigree below. a. the genotypes of the parents (I-1 and I-2) b. the probability of an offspring from the mating between individuals II-2 and II-3 having spots c. the possible genotypes of individual II-1 I II Key dark coloured sandy coloured spotted 10. A dark coloured dog is mated with a sandy coloured dog. The litter of puppies includes a dark puppy, a sandy puppy, and a spotted puppy. Use a Punnett square to determine the possible genotypes of the offspring and the parents. Note: Use the information about dog coat colour inheritance from question 9 to answer this question. Environmental Effects on Complex Patterns of Inheritance Environmental conditions often affect the expression of traits. For example, some genes are influenced by temperature. The dark colour in Himalayan rabbits, shown in Figure 6.8, is on the cooler parts of their bodies: the face, ears, tails, and feet. In these animals, dark colouring is the result of a gene that is only active below a certain temperature. One way to study the effect of the environment on expression of traits is to study genetically identical organisms placed in different surroundings. For example, identical twins are genetically identical. Differences in the activity of their genes can be due to environmental effects. SuggestedInvestigation Plan Your Own Investigation 6-A, Environmental Influences on the Production of Chlorophyll Figure 6.8 The dark ears, nose, feet, and tails of Himalayan rabbits are thought to be caused by lower body temperature in these areas. Chapter 6 Complex Patterns of Inheritance MHR 247

9 continuous variation a range of variation in one trait resulting from the activity of many genes polygenic trait a trait that is controlled by more than one gene Polygenic Inheritance Mendel carefully selected plants that had very different heights so there would be no question about phenotypes. However, there are traits that exhibit continuous variation. These are traits for which the phenotypes vary gradually from one extreme to another. Some examples of traits that show continuous variation include height and skin colour in humans, ear length in corn, and kernel colour in wheat. Continuous traits cannot be placed into discrete categories because they vary over a continuum. For example, height in humans varies over a wide range of values. People cannot be categorized as only short or tall. Traits that exhibit continuous variation are usually controlled by more than one gene. For some traits this can involve several genes. Traits that are controlled by many genes are called polygenic traits. A group of genes that all contribute to the same trait is called a polygene. Each dominant allele contributes to the trait. Recessive alleles do not contribute to the trait. For skin colour, the more dominant alleles a person has, the darker their skin. The graph in Figure 6.9 shows that there are more intermediate phenotypes than extreme phenotypes. Skin Colour Frequency aabbcc Aabbcc aabbcc aabbcc AaBbcc AabbCc aabbcc AAbbcc aabbcc aabbcc AaBbCc aabbcc AAbbCc AabbCC AABbcc aabbcc AaBBcc aabbcc AAbbCC AABBcc AaBbCC AaBBCc AABbCc AaBBCC AABbCC AABBCc AABBCC Number of Dominant Alleles Figure 6.9 This graph shows possible shades of skin colour from three of the sets of alleles that determine this trait. Predict the effect of more gene pairs on the possible phenotypes. Activity 6.1 Identifying a Polygenic Trait A polygenic trait is one that is controlled by more than one gene and shows continuous variation. In this activity, you will choose one human trait that you hypothesize is controlled by more than one gene and shows continuous variation. You will then collect data from your classmates to test your hypothesis. Materials ruler or measuring tape (if necessary) graph paper Procedure 1. In your group, choose one human trait that you think is polygenic. Make sure your choice is one for which data can be easily and respectfully collected from your classmates. 2. Construct a data table to organize your data. Keep in mind that you will be measuring a particular trait and recording the number of times that measurement of the trait occurs. 3. Collect your data from your classmates. 4. Create a line graph of your data. Your graph should reflect the actual measurements you took and the frequency of the values that you measured. Questions 1. Do your data support your hypothesis that the trait you selected is polygenic? Explain. 2. How could this activity be improved to provide a clearer picture of the inheritance pattern of the trait you selected? 248 MHR Unit 2 Genetic Processes

10 STSE Quirks & Quarks with BOB MCDONALD THIS WEEK ON QUIRKS & QUARKS Selecting for Genetic Defects Most scientists agree that certain inherited traits are favoured when they improve chances for survival. But what if improved chances for survival are due to a mutation associated with hereditary deafness? Bob McDonald interviewed Dr. David Kelsell, Professor of Human Molecular Genetics at Queen Mary College, University of London, to discuss this question. Good News and Bad News Scientists have known which gene is associated with most cases of hereditary deafness since A specific mutation in gene Cx26 (Connexin 26) is the culprit. People carrying one copy of the gene with the deafness mutation have normal hearing, while people with two copies are deaf. Because the deafness mutation in Cx26 is found in many human populations around the world, Dr. Kelsell s team suspected it must convey some kind of survival advantage. Curiously, it does seem to. Individuals with the deafness mutation also had skin that was marginally thicker than the skin of people who do not have the mutation. Tests were conducted on the mutated skin cells to see whether the deafness mutation helped skin form a better barrier against bacterial invasions, and whether the affected skin cells healed differently. Results showed that the thicker skin could offer better protection and that healing could occur much more quickly. Therefore, while there is a risk of deafness if two copies of the mutation are inherited, one copy seems to provide better protection against skin diseases. As the Quirks host said, How is it that one gene can affect two such different and seemingly unrelated things deafness and thickness of skin? This, said Dr. Kelsell, is one of the great mysteries. Related Career Human molecular geneticists study genetic processes in humans, particularly how genes function in human disease. These scientists are referred to as molecular geneticists because they look at the structure and function of genes at the molecular level. For example, they look for the effects of a genetic mutation by studying the mutant protein that is formed from it and how it affects processes in the body. Outer Ear Middle Ear Inner Ear The protein product of the Cx26 gene is needed for movement of potassium ions between cells in the cochlea of the inner ear. This movement of ions is needed for proper hearing. QUESTIONS 1. Is deafness due to a Cx26 mutation inherited by an autosomal recessive or autosomal dominant pattern? Explain your answer. tympanic membrane (or eardrum) cochlea 2. Explain why the deafness mutation of Cx26 is an example of heterozygous advantage. 3. Use the Internet or print resources to find out more about the work of human molecular geneticists. What essential skills would you need in order to work in this field? Chapter 6 Complex Patterns of Inheritance MHR 249

11 Section 6.1 REVIEW Section Summary Incomplete dominance leads to the expression of an intermediate phenotype. In the case of codominance, both alleles are fully expressed. Although an individual has only two alleles for any gene, multiple alleles for a gene may exist within the population. Environmental conditions can influence the expression of certain traits. Polygenic traits are controlled by more than one gene and can usually be identified by continuous variation in phenotype. Review Questions 1. K/U A white-flowered plant is crossed with a red-flowered plant. What is the likely mode of inheritance if the offspring produced are a. plants with pink flowers? b. plants with flowers that are red and white spotted? 2. K/U Describe a human genetic disorder that results from incomplete dominance. Explain why it is classified as incomplete dominance. 3. T/I In radishes, colour is controlled by two alleles that show incomplete dominance. When pure-breeding red radishes are crossed with pure-breeding white radishes, purple radishes are produced. a. Provide the genotypes for the three colours of radishes. b. What is the phenotypic ratio expected when two purple radishes are crossed? 4. T/I A farmer crosses a black rooster with a white hen. Of the seven offspring, three are black, three are speckled black and white, and one is white. a. What can you infer about the inheritance patterns of the alleles for white and black feathers? b. Given the inheritance pattern you described in part (a), what are the expected genotypes and phenotypes of the offspring produced by a cross between a speckled hen and a black rooster? 5. C The colour of an organism is controlled by one gene with two alleles: an allele that produces a blue colour and an allele that produces a yellow colour. Using genetic notations, describe the differences in genotypes and phenotypes of the organisms produced by crossing a true-breeding blue organism with a true-breeding yellow organism for the following three inheritance patterns. Use drawings in your answers. a. blue is dominant over yellow b. blue and yellow are incompletely dominant c. blue and yellow are codominant 6. T/I The following pedigree shows the inheritance pattern of sickle cell anemia in a family. Known carriers of the sickle cell gene are noted. However, not all individuals have been tested for the sickle cell allele. I II III Key normal phenotype, but not tested sickle cell trait (carrier) sickle cell anemia phenotype a. Determine the genotype of each individual in the pedigree. If there are any you cannot be certain of, explain why. b. Determine the probability that individuals II-3 and II-4 will have another child with sickle cell anemia. 7. T/I A chinchilla rabbit is crossed with a Himalayan rabbit, producing an albino rabbit. a. Determine the genotypes of the parents. b. Identify other phenotypes expected from this cross and give the predicted phenotypic ratios. 8. A Your friend has bred her female albino rabbit with her male Himalayan rabbit. I m hoping I ll get some agouti rabbits, she says. What are her chances of getting an agouti rabbit? Explain. 9. C Human ABO blood grouping is an example of the effects of multiple alleles, codominance, and dominance/recessiveness. Use a table or graphic organizer to explain this statement. 10. A Siamese cats that spend their lives indoors tend to have lighter-coloured fur than Siamese cats that live outdoors. What genetic process could account for this change? 11. K/U What evidence is there that skin colour in humans is a polygenic trait? 250 MHR Unit 2 Genetic Processes

12 SECTION 6.2 Inheritance of Linked Genes As you have learned, there is no apparent interaction between non-homologous chromosomes during meiosis. The movement of each pair of homologous chromosomes is independent of the movement of other pairs of homologous chromosomes. This agrees with Mendel s law of independent assortment. Recall that this law states that the alleles for a gene segregate independently of the alleles for other genes during gamete formation. However, Walter Sutton s research showing that alleles segregate in the same way that homologous chromosomes do implies a very important point: alleles on the same chromosome do not assort independently. Therefore, they do not follow the Mendelian inheritance patterns that have been discussed in this unit. It turns out that some genes are inherited together. Therefore, some traits are often inherited together or are linked. Linked Genes In 1905, William Bateson and Reginald Punnett carried out the first study that showed the movement of alleles that are on the same chromosome. Using sweet peas, they tracked the inheritance pattern of two traits: flower colour and pollen shape. They knew that purple flowers were dominant to white flowers, and that long pollen shape was dominant to round pollen shape. Their results are shown in Figure All four phenotypes that are predicted using a Punnett square were present in the F 2 generation. However, there were far more of the phenotypes from the parental generation. This suggested that the gametes produced by the parental generation, PL and pl, tended to assort together rather than independently when producing the F 2 offspring. Genes that do not assort independently are often called linked genes. Phenotype Key Terms linked genes sex-linked trait linked genes genes that are on the same chromosome and that tend to be inherited together Genotype Cross a plant with purple flowers and long pollen to a plant with red flowers and round pollen. purple flowers, long pollen Red flowers, round pollen PPLL ppll Observe the phenotypes of the F 1 offspring. PpLl purple flowers, long pollen purple flowers, long pollen purple flowers, long pollen purple flowers, long pollen Allow the F 2 offspring to self-fertilize. purple flowers, long pollen purple flowers, long pollen Meiosis PL and pl gametes more frequent Pl and pl gametes less frequent Fertilization Observe the phenotypes of the F 2 offspring. purple flowers, long pollen 15.6 purple flowers, red flowers, round pollen long pollen : 1.0 : 1.4 : red flowers, round pollen 4.5 F 2 offspring having phenotypes of purple flowers, long pollen or red flowers, round pollen occurred more frequently than expected from Mendel s law of independent assortment. Figure 6.10 A dihybrid cross between two sweet pea plants does not produce the expected phenotypic ratio of 9:3:3:1. These results support the theory that alleles on the same chromosome do not assort independently. Identify Provide the genotypes of the F 2 offspring. Chapter 6 Complex Patterns of Inheritance MHR 251

13 Crossing Over and the Inheritance of Linked Genes A chromosome may contain up to a few thousand genes. All of the genes on any one chromosome are called a linkage group because they tend to be inherited together. However, linked genes do not always stay linked researchers have found that they segregate on a regular basis. This is due to the process of crossing over, which you learned about in Chapter 5. Recall that crossing over occurs in prophase I of meiosis, when non-sister chromatids exchange pieces of chromosomes. Suppose you are studying two genes that are on the same chromosome and, therefore, linked. Crossing over between homologous chromosomes can occur. As shown in Figure 6.11, this will result in the alleles of the linked genes no longer being on the same chromosome. The alleles of the previously linked genes are now unlinked. This means that they will migrate into different gametes. The result is that instead of two types of gametes being produced, four different types of gametes will be produced in differing proportions. There are fewer gametes with the recombined alleles because crossing over is a random event and it occurs infrequently. A a Figure 6.11 In most of the gametes formed, there is no crossing over they maintain the linkage of the alleles. In a small minority of gametes, crossing over occurs and alleles of previously linked genes become unlinked. Describe why alleles of genes that are closer together on a chromosome are more likely to remain linked during meiosis. A no crossing over during meiosis a B b crossing over during meiosis a A B 97% b B 3% recombinant gametes b four types of gametes in unequal proportions Using Gene Linkage for Chromosome Mapping Scientists have discovered that alleles for a given pair of linked genes will separate with a predictable frequency and that this frequency is different for different pairs of linked genes. The frequency depends on how close the alleles of the linked genes are positioned on a chromosome. Crossing over occurs more frequently between alleles that are far apart on a chromosome than between alleles that are close together. Therefore, a given pair of linked genes will separate more frequently than the alleles for another pair of linked genes if their alleles are farther apart on the chromosome. This process of determining the relative locations of genes on chromosomes is called chromosome mapping. These types of linkage studies are useful for mapping chromosomes in species that reproduce rapidly and produce many offspring, such as plants and insects. But chromosome mapping is not useful in mapping human chromosomes. Chromosome mapping of humans only became possible when modern techniques that allow scientists to directly see the chromosomes became available. 252 MHR Unit 2 Genetic Processes

14 Learning Check 7. What are linked genes? 8. How are linked genes found experimentally? 9. What is chromosome mapping? How is gene linkage used in chromosome mapping? 10. Suppose that two individuals with the genotype AaBb are crossed, and the phenotypic ratio produced is about 3:1 (A_B_:aabb). Are the genes for the two traits linked? Explain. 11. Some traits are described as being due to sex-linked genes. Use your knowledge of chromosomes to explain what this means. 12. Many genetic tests are based on analyzing genes that are linked to alleles that cause disease. Explain how testing for a linked gene could lead to an incorrect diagnosis. Sex-linked Inheritance An American biologist named Thomas Hunt Morgan, shown in Figure 6.12, originally did not accept Sutton s chromosome theory of inheritance. In the early 1900s, Morgan chose to do research on the fruit fly, Drosophila melanogaster, to develop a new and alternative theory. Morgan chose this organism because it is economical to maintain, reproduces rapidly, and has traits that are fairly easy to characterize. As Morgan collected data, however, his results soon convinced him that Sutton s theories were correct. Nevertheless, Morgan s meticulous research provided additional information about genetic inheritance. In 1910, Morgan discovered an unusual white-eyed male among his fly population. He crossed the white-eyed male with a normal red-eyed female. All the F 1 generation had red eyes. This seemed to indicate that normal red eyes are dominant to the white-eye mutation. When Morgan crossed a male and female from the F 1 generation, however, the results surprised him. All the females of the F 2 generation had red eyes, half the F 2 males had red eyes, and half the F 2 males had white eyes. The discovery that the gene for eye colour was connected to gender led Morgan to conclude that the gene for eye colour is located on the X chromosome. Like humans, female fruit flies have two X chromosomes, while males have one X chromosome and one Y chromosome. The fruit fly F 1 data indicated that the white-eye phenotype is recessive, since it was masked in all of the offspring in that generation. How did white eyes reappear in only the male fruit flies in F 2, but remain masked in the female flies? The answer lies in the sex-linked genes the genes that are located on the X and Y chromosomes. Traits that are controlled by genes on either the X or Y chromosome are called sex-linked traits, because they are linked to the genes that determine sex. They are identified by their different rates of appearance between males and females. sex-linked trait a trait controlled by genes on the X or the Y chromosome Figure 6.12 (A) Drosophila melanogaster traits that are often studied include eye colour and wing size and shape. Males and females can be easily identified. (B) Thomas Morgan s ground-breaking research into the genetics of fruit flies was recognized in 1933, when he was awarded the Nobel Prize in physiology or medicine. A B female male Chapter 6 Complex Patterns of Inheritance MHR 253

15 Sex-linked Genes The X and Y chromosomes, although paired together during meiosis and for karyotyping purposes, have very little homologous DNA. The X and Y chromosomes in humans have only a few genes in common. The human X chromosome is estimated to contain about 2000 genes, while the Y chromosome contains fewer than 100. The most important genes are the sex-determination genes. For all other genes on the X chromosome, females have two copies, while males have only one. This allows for the difference in the expression of traits for genes that are found on the X chromosome, which are often called X-linked genes. By comparison, only a few genes are known to be Y-linked, because there are significantly fewer genes on the Y chromosome. When considering sex-linked traits, the allele on the sex chromosome is shown as a superscript to an X or a Y. The Red and White Eyes of Fruit Flies Red and white eyes were the first sex-linked trait explored by Morgan. The possible genotypes and phenotypes in both males and females are listed in Table 6.1. X R indicates red eyes, which is the dominant phenotype, and X r indicates white eyes, which is the recessive phenotype. Notice that female flies may be a carrier for the white-eye phenotype. However, if the allele for white eyes is present in males, it will always be expressed. This means that X-linked traits are exhibited more often in males. Punnett squares can be used to predict the outcome of crosses that involve sex-linked traits. Figure 6.13 represents some of the crosses that Morgan studied. Table 6.1 Possible Genotypes and Phenotypes for Drosophila Eye Colour SuggestedInvestigation ThoughtLab Investigation 6-B, Sex-Linked Crosses Genotype X R X R X R X r X r X r X R Y X r Y Phenotype Female with red eyes (homozygous dominant) Female with red eyes (heterozygous, carrier for the white-eyed allele) Female with white eyes (homozygous recessive) Male with red eyes Male with white eyes X R red-eyed female X R X R X R X R F 1 female X R X r X r X r X R X R X r X R X r X R X R X R X r white-eyed male X r Y Y X R Y X R Y F 1 male X R Y Y X R Y X r Y Figure 6.13 In Morgan s experiment on tracking the inheritance pattern of a sex-linked trait, the white-eye phenotype was passed from the father in the P generation through the daughter in the F 1 generation. Predict the genotype and phenotype ratios of the offspring created by crossing a white-eyed male and a heterozygous female. 254 MHR Unit 2 Genetic Processes

16 Sex-linked Traits in Humans Some examples of sex-linked traits in humans are listed in Table 6.2. As you can see, many are genetic disorders. If a disorder is X-linked dominant, affected males pass the allele only to daughters, who have a 100 percent chance of having the disorder. Females can pass an X-linked dominant allele to both sons and daughters, all of whom will have the disorder. Most sex-linked inherited traits in humans are X-linked recessive traits. Therefore, while the male only needs to inherit one allele to be affected, the female must inherit both alleles to be affected. Thus, X-linked recessive traits affect more males than females in a family. Table 6.2 Sex-linked Traits in Humans Condition Inheritance Pattern Description Red-green colour vision deficiency (CVD) Duchenne muscular dystrophy X-linked recessive X-linked recessive Cannot distinguish between certain shades of red and green Progressive weakening of muscles and loss of coordination Hemophilia X-linked recessive Cannot produce a necessary blood clotting factor Adrenoleukodystrophy X-linked recessive A build-up of fatty acids that causes progressive brain damage and death X-linked severe combined immunodeficiency (SCID) X-linked recessive Decreased immune response due to low white blood cell counts X-linked hypophosphatemia X-linked dominant Softening of bone, which leads to bone deformity Hairy ears Y-linked Hair grows on the outside of the ears Colour Vision Deficiency: An X-linked Recessive Trait In humans, there are inherited forms of colour vision deficiency (CVD). Individuals affected by CVD have varying degrees of difficulty distinguishing between different colours or shades of colours. One form, called red-green CVD, is an X-linked recessive disorder. Individuals with red-green CVD have difficulty distinguishing between shades of red and green. To track the inheritance patterns of sex-linked traits in humans, pedigrees are often used. The inheritance pattern of red-green CVD in one family is shown in Figure I II X B X B X b Y X B Y X B X b X B Y X b X b Key X B X B = normal female X B X b = carrier female X b X b = CVD female X B Y = normal male X b Y = CVD male X b Y III X B Y X B X B X B X b X b Y Figure 6.14 An X-linked recessive trait like CVD will affect more males than females in a family. Chapter 6 Complex Patterns of Inheritance MHR 255

17 Figure 6.15 Great Britain s Queen Victoria was a carrier for hemophilia. Hemophilia: A Common Sex-linked Trait in Humans Hemophilia is a condition that affects the body s ability to produce proteins involved in blood clotting. People with hemophilia can suffer serious blood loss from simple cuts and bruises. Hemophilia is an X-linked recessive trait that affects more than 3000 individuals in Canada. Hemophilia is often referred to as the royal disease because it spread among the royal families of Europe, through the descendents of Great Britain s Queen Victoria, shown in Figure Queen Victoria was a carrier who passed the allele on to some of her offspring. Arranged marriages among royalty of Europe were very common until the twentieth century. Pedigree analyses can trace the allele for hemophilia throughout the royal families of Spain, Russia, and Prussia. Sample Problem Using Punnett Squares to Analyze Sex-linked Inheritance Patterns Problem Determine the probability that a woman who is a carrier for hemophilia and a man without hemophilia will have a child with hemophilia. What Is Required? You need to determine the possible genotypes and phenotypes of the offspring to determine if any of the children could have hemophilia. What Is Given? You know the phenotypes of the parents, and you know that the pattern of inheritance is X-linked recessive. Plan Your Strategy Assign letters to represent each allele for the trait, and then determine the genotypes for the parents based on an X-linked recessive inheritance pattern. Use a Punnett square to predict the genotypes of the offspring. Act on Your Strategy Since the inheritance pattern is X-linked recessive, let X h = allele for hemophilia let X H = allele for normal blood clotting The female is a carrier, so her genotype is X H X h. The male is unaffected, so his genotype is X H Y. male X H Y female X H X h Complete the Punnett square. male female X H X h X H X H X H X H X h Y X H Y X h Y Determine the predicted phenotypes of the offspring, and the probability of producing a child with hemophilia. There is a 25 percent chance of having a child with hemophilia (X h Y). All other genotypes produce a child with normal blood clotting. Check Your Solution To check your solution, ensure that the genotypes of the parents accurately represent the phenotypes, and that all possible combinations of gametes have been made. 256 MHR Unit 2 Genetic Processes

18 Sample Problem Determining Sex-linked Inheritance Patterns in a Pedigree Problem The pedigree on the right shows the inheritance of red-green CVD in a family. Identify the genotype of each family member represented in the pedigree. How does the inheritance pattern in the pedigree support X-linked inheritance? What Is Required? You need to determine the genotype of each individual and describe the evidence for X-linked inheritance. What Is Given? You know that the pattern of inheritance is X-linked recessive, and you have the phenotype of each of the individuals (the pedigree). I II III Plan Your Strategy Assign letters to represent each allele. Identify possible genotypes for each of the phenotypes based on an X-linked recessive inheritance pattern. Assign all possible genotypes, according to the information in the pedigree. At this point, you cannot be certain of the genotypes for individuals I-1, II-1, and II-3. Since they are unaffected females, the possible genotypes are X C X c and X C X C. Act on Your Strategy let X c = allele for CVD let X C = allele for normal vision X C X C = unaffected female X C Y = unaffected male X C X c = female carrier X c Y = male with CVD X c X c = female with CVD I II X c Y 1? X C Y? ? 2 X C Y III X C Y 1 X C Y X C Y X c Y Complete the pedigree with genotypes that you can infer based on the data in the pedigree. You know that individual II-3 must be X C X c to produce a son who has CVD. Individual II-1 must be X C X c. The X chromosome she received from her father is X c and, since she is unaffected, she must have received X C X c from her mother. You cannot be certain of the genotype of I-2 because both genotypes are possible (X C X c and X C X C ), given the genotypes of the offspring. Describe how the inheritance pattern supports X-linked recessive inheritance. I II III X C Y 1 X C X c 1 X C Y X C Y X c Y X C Y 2 3 4? 2 X C X c X c Y X C Y The allele for CVD is passed from the grandfather (I-1) through his unaffected daughter (II-3) to her affected son (III-4). This pattern is indicative of X-linked recessive inheritance. As well, more males are affected than females, which also indicates X-linked recessive inheritance. Check Your Solution To check the pedigree, ensure that all the offspring genotypes are possible given the genotypes of the parents. Chapter 6 Complex Patterns of Inheritance MHR 257

19 Practice Problems 11. A woman who is a carrier for CVD and a man who has CVD decide to have children. a. Determine the genotypes of these two people. b. What is the expected ratio of genotypes and phenotypes among their children? 12. The mother and father of a boy who has CVD both have normal colour vision. Use a Punnett square to explain how this can occur. 13. A woman with hemophilia and a man without hemophilia decide to have children. What is the probability that their sons will have hemophilia? 14. Nystagmus is a condition in which involuntary eye movement leads to poor vision. This condition is caused by an X-linked recessive allele. Suppose that a man and woman, both with normal vision, have two children. The boy is affected with nystagmus, and the girl is unaffected. a. Determine the genotype of the parents. b. Is it possible to determine the genotypes of the children? Why or why not? 15. A woman has X-linked hypophosphatemia, which affects bone development. She marries a man with normal bone structure. If the woman s father also has normal bone structure, what is the probability that the woman and her husband will have a child with the disorder? 16. A true-breeding tan-bodied female fruit fly is crossed with a yellow-bodied male. All of the offspring in F 1 have tan bodies. In the F 2 generation, all the females have tan bodies, 50 percent of the males have tan bodies, and 50 percent of the males have yellow bodies. a. Describe the pattern of inheritance for body colour in fruit flies. Explain your answer. b. Determine the genotypes of the flies described in the F 2 generation. c. What is the probability of producing tan offspring from a yellow female and a tan male? 17. Given the pedigree below, determine whether the pattern of inheritance of this trait is X-linked recessive, X-linked dominant, or Y-linked dominant. Explain your answer. I II III In one breed of dog, a mutant gene that causes hearing impairment is found on the Y chromosome. What are the possible phenotypes of offspring from each of the following crosses? a. a male dog whose father is hearing impaired and a female dog whose father is not hearing impaired b. a female dog whose father is hearing impaired and a male dog whose father is not hearing impaired 19. Suppose you have one homozygous dominant red-eyed female fly and one white-eyed male fly. What steps would you follow to produce a white-eyed female fly? 20. The allele for short fingers is dominant to the allele for long fingers. What is the genotype of a male who has CVD and long fingers? If all of his children have normal vision and short fingers, what is the likely genotype of the children s mother? Figure 6.16 In cats, the alleles for black or orange coat are carried on the X chromosome. Barr Bodies: Inactive X Chromosomes Since females carry two X chromosomes and males only one, why is there no difference in the expression of X-linked genes between males and females? The answer is that every cell has only one functioning X chromosome. In every female cell, one of the X chromosomes is inactive. The inactive X chromosome is condensed tightly into a structure known as a Barr body. At an early stage of embryonic development, one X chromosome in each cell is deactivated. Which X chromosome is deactivated can vary among cells. One visible effect of one X chromosome being inactive is the calico, or tortoiseshell, coat colour in cats, shown in Figure In heterozygous females, roughly 50 percent of the cells have an active X chromosome with the allele for black coat colour, and 50 percent of the cells have an active X chromosome with the allele for orange coat colour. This results in a tortoiseshell coat with patches of both black and orange. The patches of white are the result of the interaction with a different gene. 258 MHR Unit 2 Genetic Processes

20 Section 6.2 REVIEW Section Summary Alleles of different genes that are on the same chromosome do not assort independently. These genes are said to be linked and their associated traits tend to be inherited together. Sex-linked traits are expressed in different ratios by male and female offspring because they are determined by the segregation of X and Y chromosomes. Although sex-linked genes are linked to the X and Y chromosomes, Punnett squares can be used to predict genotypes and phenotypes. Review Questions 1. T/I Design an experimental procedure that you could follow to determine whether two plant genes are linked. 2. K/U Describe how the process of crossing over of non-sister chromatids can affect linked genes. 3. K/U What experimental evidence would lead scientists to suspect that two genes are linked? 4. T/I A chromosome contains three genes, P, Q, and R. The percentage of gametes produced that have the genes separated due to crossing over is shown in the table below. Linked Genes Gametes with Genes Unlinked Genes (%) P and Q 5 P and R 18 Q and R 13 From these data, identify the gene pair with alleles that are closest together on the chromosome. Explain your answer. 5. C Draw a diagram that shows how crossing over can cause linked genes to become unlinked. 6. K/U List two features of Drosophila melanogaster that make this species a good choice for the study of sex-linked inheritance. 7. T/I A woman with regular vision and a man with regular vision have three children, one of whom has CVD. a. What can you conclude about the genotypes of the parents? b. What sex is the child who has CVD? How do you know? 8. K/U Describe the possible genotypes of the parents of a woman who has hemophilia. Explain your answer. 9. A Explain how a girl with Turner syndrome could have red-green CVD, even though both of her parents have normal vision. 10. T/I The following pedigree was given to a group of students to analyze. They believe it indicates X-linked recessive inheritance. Do you agree or disagree? Explain your answer. I II III K/U How do pedigrees for autosomal recessive traits and X-linked recessive traits differ? 12. C A boy has Duchenne muscular dystrophy. His mother s brother also has this disorder. The boy s father and his two younger sisters do not appear to be affected by the disease. Draw a pedigree to illustrate the inheritance of Duchenne muscular dystrophy in this family. What is the probability that his sisters are carriers of the disease? 13. K/U The symptoms associated with X-linked dominant diseases are often more severe in males. Explain. 14. C Draw a sample pedigree to illustrate inheritance of hemophilia in a family. Make sure that your pedigree reflects that particular inheritance pattern. 15. A Some women are heterozygous for an X-linked genetic disorder that results in a non-uniform distribution of sweat glands on their skin. These women have patches of skin that lack sweat glands and patches of skin that have sweat glands. How can the Barr body cause this phenomenon? Chapter 6 Complex Patterns of Inheritance MHR 259

21 SECTION 6.3 The Future of Genetics Research Key Terms bioinformatics genomics genetic profile Figure 6.17 The Human Genome Project achieved many milestones and has provided a springboard for decades of future research. Nevertheless, this project would not have been possible without several essential preceding discoveries including Mendel s studies of pea plants. Genetics research is continually changing and developing in response to new discoveries. Many genetics researchers now focus on obtaining more and more detailed information. In addition to wanting to know the sequences of genes that are associated with certain inherited traits, investigators want to know how those genes play a role in determining those particular traits. Looking for answers to these types of questions has led to the development of more sophisticated technologies and equipment, and has resulted in new scientific fields of study. In addition, many studies now require the collaboration of scientists from very different disciplines, such as biology, chemistry, physics, sociology, bioethics, and political science. The Human Genome Project In the opener for this chapter, you were introduced to the the Human Genome Project. Determining the DNA sequence of the human genome is considered to be one of the most pivotal contributions to science ever made. Nevertheless, achieving this scientific landmark depended on many discoveries that came before it. Figure 6.17 highlights only a small number of developments since Mendel s work that formed the foundations of this project. An important component of the 13-year Human Genome Project was determining the DNA sequences of other organisms. This allows scientists to make comparisons between species and learn even more about important features of genomes. Overall, identifying the genome sequences of humans and many other organisms allows for a much more comprehensive understanding of biological systems. This knowledge will have a wide range of applications in fields such as human health, agriculture, and the environment. rediscovery of Mendel s work DNA as the hereditary material is identified Gregor Mendel discovers laws of genetics the first linear map of genes is produced the structure of DNA is determined the genetic code is identified the Human Genome Project is launched ethical, legal, and social implications (ELSI) program founded first US genome centres established rapid-data-release guidelines established US Equal Employment Opportunity Commission issues policy on genetic discrimination in the workplace yeast (Saccharomyces cerevisiae) genome sequenced Escherichia coli genome sequenced 260 MHR Unit 2 Genetic Processes

22 What s in Our Genome? In addition to determining the actual sequence of the nucleotides in the human genome, scientists had to make sense of the sequence. Trying to make sense of the sequence can be compared to reading a book written in a language nobody knows or understands. Imagine the genome as words in a book written without capitalization, punctuation, or breaks between words, sentences, or paragraphs. Also, suppose there are strings of additional letters scattered randomly between and within sentences. Figure 6.18 shows how a page from such a book might look. To understand what is written, you have to decode the jumbled text. Similarly, scientists had to decode the sequence of our DNA to learn about the human genome. When the Human Genome Project began, there was a great deal that was not known about our genome. For example, it was not known how many genes humans actually had and how much of our DNA is part of those genes. After sequencing the entire human genome, scientists observed many things that surprised them. Some of these discoveries include the following: Figure 6.18 Decoding the DNA sequence of the human genome is like figuring out where the punctuation and capitalization must go to understand what is written on this page. Only about 2 percent of the nucleotides in the human genome make up our genes and code for all the proteins in the body. The estimated total number of genes is much less than scientists predicted. Previous estimates were between and Over 50 percent of our DNA consists of stretches of repeating sequences. There is very little genetic variation within our species. About 99.9 percent of the DNA sequence is almost exactly the same in all people. Having the sequence of the human genome only represents a starting point. It is like being given the pages of an instruction manual for the human body. The next steps involve figuring out how to interpret all of the information and use that to understand how everything works together. Scientists agree that this process will take many more years of research. methods for determining the sequence of DNA are developed 1972 cystic fibrosis gene is identified recombinant re DN DNA technology is developed 1989 Human 1990 Genome Project 2003 first human disease gene for Huntington disease is mapped full-scale human genome sequencing begins free access to genome information established sequence of first human chromosome (chromosome 22) completed fruit fly ((Drosophila melanogaster) genome sequenced draft version of human genome sequence ce published sequences of mouse, rat, an and rice genomes completed human genome sequence completed mustard s ard cress sta (Arabidopsis opsis thaliana) op genome e sequenced Chapter 6 Complex Patterns of Inheritance MHR 261

23 bioinformatics a field of study that deals with using computer technology to create and analyze large databases of information Figure 6.19 A chemist named Margaret Dayhoff is considered to be the founder of bioinformatics. The Development of Bioinformatics In the Launch Activity at the beginning of this chapter, you simulated the work required to piece together the sequence of a small fragment of DNA. Imagine doing this work by hand for the over three billion base pairs of the human genome. Sequencing the human genome and the genomes of other organisms generated exceptionally large amounts of data that needed to be organized and shared among labs around the world. A new field of study, called bioinformatics, arose from this need. Bioinformatics is a branch of biology that deals with applying computer technology to create and maintain databases of information that can be analyzed to better understand biological processes. Bioinformatics is a relatively new branch of biology. American chemist Margaret Dayhoff, shown in Figure 6.19, is the founder of bioinformatics. Her work, which began in the late 1940s, involved creating a computerized protein and DNA sequence database the first bioinformatics project. Today s bioinformatics exists because of simultaneous advances in three areas: techniques to sequence biological molecules such as DNA and proteins, computer database software to sort and store massive amounts of genetic information, and communication technology to share information around the world efficiently. Today, there are many on-line genetics databases available that allow easy access to vast amounts of genetic information by all members of the public not just scientific researchers. Bioinformatics is just one of a number of newly developed fields, all of which involve using computers to study biological problems. For example, computational biology involves developing mathematical models and computer simulations of biological processes. Activity 6.2 Accessing Genetic Information In this activity, you will join the worldwide community of scientists who explore information stored in the many on-line databases that are available. Materials computer with Internet access Procedure 1. Choose one of the genetic disorders provided by your teacher. 2. Use the Internet to access the website that you will be using. Your teacher will provide a demonstration to help you get started. 3. Spend some time looking at the different databases that are available from this site. What different types of information about a genetic disorder can be obtained from them? 4. Choose three or four types of information that are available about the genetic disorder that you selected. Questions 1. Summarize the information you collected on the genetic disorder you investigated. 2. Based on your experience with the on-line databases, what was the most effective way of obtaining the information that you were looking for? Learning Check 13. What were some achievements of the Human Genome Project? 14. How much of the human genome is actually used to code for proteins? 15. List three types of technologies that contribute to developing the tools used in bioinformatics. 16. Explain how bioinformatics contributed to the Human Genome Project. 17. Why was development of the Internet crucial for the Human Genome Project? 18. Describe an experiment that requires bioinformatics. 262 MHR Unit 2 Genetic Processes

24 Genomics: The Study of Genomes Just as genetics is the study of genes, genomics is the study of genomes and how genes work together to control phenotype, as illustrated in Figure Although some traits are determined by only one gene, most traits involve multiple genes. To understand how an individual gene produces a specific phenotype, researchers such as Mendel and Morgan chose one gene and studied it and its phenotype across many individuals. A significant advantage that came from the Human Genome Project was the ability to consider multiple genes and the genome as a whole. This allows scientists to study the interactions among many genes and how they all contribute to a phenotype. Computer technology and fields such as bioinformatics play a vital role in this by allowing scientists to analyze large amounts of information from a variety of sources. Although there is considered to be little variation in the sequence of the human genome, it is important to keep in mind that the 0.1 percent difference represents potential for variation in about three million nucleotides. Some of this variation is associated with many diseases. Scientists believe that almost all human diseases have a genetic component, either directly or indirectly. Comparing genome sequences has been particularly useful in studying the genetic basis for many human diseases, such as cancer. For example, bioinformatics and computational biology have been used to compare the DNA sequences of certain regions of the genome in individuals affected by a particular type of cancer with the DNA sequences of the same regions in those who are not. Differences in DNA sequence indicate a potential genetic basis for the disease. While this represents a good starting point for the study of the genetics of a disease, scientists are discovering that many diseases are the result of a complex array of factors, and studying them requires more elaborate methods. genomics the study of genomes and the complex interactions of genes that result in phenotypes C G T T C T C T A T T A A C A... G C A A G A G A T A A T T G T... three billion DNA base pairs in the cell nucleus phenotypes are expressed thousands of different proteins are produced in trillions of cells Figure 6.20 Genomics is the study of how an organism s genome contributes to its phenotype. Chapter 6 Complex Patterns of Inheritance MHR 263

25 Linking Genetic Variations to Disease In previous sections, you learned about diseases that are associated with a mutation or mutations in a single gene, such as sickle cell anemia. Many other diseases, such as cancer, stroke, heart disease, diabetes, and asthma, are influenced by a combination of environmental and genetic factors. Many scientists consider determining what variations in DNA sequence contribute to different diseases to be one of the best opportunities to understand the complex causes of many human diseases. The most common type of variation between people is differences in individual nucleotides, as shown in Figure For example, one person may have a C at a certain location, while another person may have a T. This type of genetic variation is called a single nucleotide polymorphism, or SNP (pronounced snip ). A SNP can act as a marker for a gene or be associated with a gene if it is genetically linked to it. Recall that sequences of DNA are genetically linked when they are physically close to each other on a chromosome and tend to be inherited together. For example, if a SNP is common among people with high blood pressure, that could provide a marker for the location of a gene that is involved in the disease. However, there are almost 10 million different SNPs that commonly occur in the human genome. Testing all of these is not feasible. Nevertheless, SNPs that are near each other on a chromosome tend to be inherited together. These regions of genetically linked variations are called haplotypes. Certain tag SNPs can uniquely identify these haplotypes. Since there are far fewer of these types of SNPs, they can be used as a basis for comparing genetic variations and identifying genes that influence the health of an individual. In 2002, an international group of researchers from Canada, the United States, Japan, China, Nigeria, and the United Kingdom collectively began the International HapMap Project. The major aim of this project is to develop a haplotype map (HapMap) of the human genome, which represents a map of the variations in the human genome. This can then be used by other scientists to identify the genetic basis for many human diseases. SNP SNP SNP Chromosome 1 Chromosome 1 Chromosome 1 Chromosome 1 A A C A C G C C A.... A A C A C G C C A.... A A C A T G C C A.... A A C A C G C C A.... T T C G G G T C T T C G A G T C T T C G G G T C T T C G G G T C A G T C G A C C G.... A G T C A A C C G.... A G T C A A C C G.... A G T C G A C C G.... Haplotype map of the human genome Figure 6.21 A haplotype map is constructed by identifying single nucleotide polymorphisms (SNPs) among a number of individuals. Beyond the Genome Sequence Analysis of the data generated from the Human Genome Project will continue for many decades. A significant part of that research involves more than working at the level of the DNA sequence. For example, the field of proteomics began when scientists recognized how important it is to understand the products of our genes proteins. Based on the term genome, the term proteome was developed to refer to all of the proteins in an organism. Research studies in proteomics focus on studying the three-dimensional shape of proteins and eventually determining the functions of all the cellular proteins. 264 MHR Unit 2 Genetic Processes

26 Studying Gene Expression Today, many scientists are studying what regulates the expression of genes. That is, they look at what influences whether a particular protein is produced from a certain gene and, if so, how much of the protein is made. An individual s phenotype is the result of which genes are active are being expressed and which genes are inactive, or not being expressed. While all cells of an individual have the identical genetic material, the same genes are not expressed in the same way in every type of cell. For example, differences in gene activity can exist between healthy cells and cells of diseased tissue, such as cells of cancerous tumours. Scientists now realize that some factors that affect gene expression can be inherited, but they are not due to changes in DNA sequence. Epigenetics is the study of how changes in the inheritance of certain traits or phenotypes are based on changes to gene function and not to changes in DNA sequence. Epigenetics differs from evolution because there is no change to the DNA sequence of a gene and epigenetic changes are not necessarily permanent. Epigenetic changes represent a response to an environmental condition that may be reversed once that condition changes, or soon after the change. The term epigenome refers to cellular material that is not part of the genome but that influences whether a gene is turned on or turned off. Identifying epigenetic factors is believed to be a next major frontier in biological sciences. Studying Gene Expression Using Microarrays A very important method that is used to study differences in gene activity is DNA microarray technology. In this technique, DNA is placed as spots on a glass plate, called a microarray plate. One slide can contain thousands of spots of DNA that correspond to certain parts of a genome, and that contain different genes. Figure 6.22 shows an example of a microarray plate. This technique allows scientists to study the activity of up to thousands of genes at a time, under particular conditions. Studying the activity of so many genes at once tells scientists which genes are active or inactive under certain conditions, and gives them information on how this activity is co-ordinated among different genes. Figure 6.22 DNA microarrays allow scientists to see the activity of genes under certain conditions. The colour of each circle on a microarray plate like this one corresponds to the activity of a gene in the DNA spot on the plate. Chapter 6 Complex Patterns of Inheritance MHR 265

27 genetic profile the complete genotype of an individual, including various mutations Genetic Information: Public Benefits and Concerns Some of the most important benefits of genetic research are in the area of human medicine. Figure 6.23 illustrates this link between genetics and medical treatment. Studying the human genome as a whole may make it possible to develop drugs that are tailored to the expression of the genes associated with particular disorders, and to the unique genome of a patient. In the future, researchers hope to use established links between genetic variation and risk of disease to provide better medical advice to patients. If the cost of DNA sequencing continues to decrease, individuals may have access to their genetic profile their complete genotype, including all of the various mutations linked to disease. Currently, doctors are only able to make generalized risk assessments based on medical history. Armed with a genetic profile, however, genetic counsellors and doctors will be able to provide more specific risk assessments, design individualized prevention plans, and design genetically precise treatment programs. Figure 6.23 This altered representation of the caduceus a common symbol for medical practice illustrates the link between genetics and treatment of disease. What Can Happen to Information from a Genetic Profile? Establishing genetic profiles for individuals, and making these profiles available to health-care providers, also creates ethical concerns. For example, Could insurance companies deny coverage to people who have a genetic predisposition for a particular disease? Could potential employers have access to an individual s genetic profile and use it in assessing whether to hire the person? Should researchers be allowed to use the genetic profiles of individuals to help them better understand the link between genome and phenotype? The central issue in all of these ethical questions is who should have access to the information in a genetic profile. Ownership of Genetic Information All the data gathered through the Human Genome Project is publicly available. Having access to the data made it possible for scientists to share what they learned about human genetics. In other areas of genetics research, however, the relationship between public and private information is more complex. In 2005, the National Geographic Society and the IBM company jointly launched the Genographic Project. This project uses DNA samples provided by hundreds of thousands of volunteers around the world to learn more about the migrations of ancient peoples. Using high-tech genetics tools and computer facilities, DNA sequences of the individuals are analyzed to better understand human genetic roots and how we all connect at the level of our DNA. Studies such as the Genographic Project can contribute valuable information to researchers in many fields. But who owns the genetic information? For example, should companies have the right to sell DNA information to other companies without the permission of the people who provided the samples? Should companies that use DNA in medical research be required to share the results of their work with the individuals or communities whose genetic information was used? Some people argue that genetic information is a natural resource that belongs to everyone. Others believe that genetic information about a person belongs only to that person. In addition, many think that if companies cannot earn a profit from their research, there is little incentive for them to invest in genetic studies. In the world of genetics research, where is the boundary between public and private property? 266 MHR Unit 2 Genetic Processes

28 Section 6.3 REVIEW Section Summary The complete DNA sequence of the human genome was determined as part of the Human Genome Project. The field of bioinformatics arose from the need to share and maintain the large quantities of data collected from genomic research. It also provides tools for analyzing genomic data. There is still much to be learned from the data generated from the Human Genome Project, particularly in identifying genes that are associated with human health. Current and future research in genomics may allow scientists to tailor preventative and curative treatments for individual patients based on their specific genetic profiles. However, ethical questions about who owns an individual s genetic information continue to be debated. Review Questions 1. K/U The Human Genome Project involved sequencing the genomes of other organisms as well as of humans. Provide two reasons for why this was done. 2. C In this section, the human genome was compared to a book. Illustrate how the parts of a book pages, paragraphs, sentences, words, and letters can be used to represent chromosomes, chromatids, genes, and nucleotides. 3. K/U Describe three things about the human genome that scientists learned from the Human Genome Project. 4. K/U Although the Human Genome Project is complete, research based on its findings continues. Describe two areas of current research that developed from it. 5. A The Human Genome Project cost billions of dollars to complete. Do you think it was worth it? Provide reasons that support your opinion. 6. T/I The two pictures below show scientists conducting genetic research in labs. The photo on the left was taken in the 1980s, and the photo on the right was taken in the 2000s. Describe how these photos reflect the changes in genetic research that took place over this time period. 7. T/I Describe why you think the field of bioinformatics was given that name. Provide a suitable alternative name for this field of science. 8. K/U What is genomics? Describe the type of research that is involved and how it may help society. 9. K/U What is the HapMap project? What is its main goal? 10. T/I Explain how epigenetics suggests that the traits we inherit may not be due only to the DNA we receive. 11. K/U Describe how DNA microarray technology is used to study gene expression. 12. C Determining a genetic profile can have its benefits and its risks. Use a table to list as many benefits and risks as you can. 13. C Should people be encouraged to have their genetic profiles determined, since this might prevent them from developing certain illnesses? Justify your answer using examples. 14. A Imagine that you have been hired by an international organization that establishes practices for scientists to follow when doing genetics research. Your job is to develop a policy on the collection and ownership of genetic information. a. What are some of the issues you should consider? b. Based on the issues you listed, decide where you stand on those issues and develop a policy that reflects that stance. c. Briefly summarize how your policy will balance public and private interests. 15. C Write a paragraph expressing your opinion on whether employers should have to provide a work environment that suits a person s genetic profile. Chapter 6 Complex Patterns of Inheritance MHR 267

29 Plan Your Own INVESTIGATION 6-A Skill Check Initiating and Planning Performing and Recording Analyzing and Interpreting Communicating Safety Precautions Wash your hands when you have completed this investigation Suggested Materials seeds (Brassica rapa, radish, or bean) labels paper towels water shoe boxes petri dishes graduated cylinder light source Environmental Influences on the Production of Chlorophyll Chlorophyll is the molecule that allows plants to capture light energy from the Sun and use the energy to produce food in the form of sugars. Chlorophyll is also the pigment that gives leaves their green colour. Plants that produce chlorophyll appear green. If the production of chlorophyll is turned off, the plant will become pale yellow, or even white. The production of chlorophyll is under genetic control. Working in groups and using the materials provided, you will design and conduct an investigation to test the influence of light on the production of chlorophyll. Your investigation must enable you to draw conclusions about each of the following. What is the minimum duration of exposure to light required to turn on the production of chlorophyll? Is the triggering event reversible? That is, does chlorophyll production start and stop as environmental conditions change? Go to Organizing Data in a Table in Appendix A for help with designing a table for data. Go to Constructing Graphs in Appendix A for information about making graphs. When chlorophyll is no longer present, a green plant will become pale yellow or even white. This is similar to what happens to many trees during the autumn. In the spring and summer, tree leaves appear green because chlorophyll is being produced. With the change in environmental conditions that accompanies autumn, chlorophyll is no longer produced and other pigments in the tree leaves become visible. This results in the yellow, orange, and red fall colours of some trees. 268 MHR Unit 2 Genetic Processes

30 Pre-Lab Questions 1. Describe the genotype of the organisms you should use that will allow you to test the effect of the environment on phenotype. 2. What is the difference between qualitative and quantitative data? 3. Differentiate among independent, dependent, and controlled variables. Question How does light influence the production of chlorophyll in germinating plants? Hypothesis Formulate a hypothesis to explain how light influences the activity of the genes responsible for chlorophyll production. Use this hypothesis as the basis of your experimental design. Plan and Conduct 1. With your group, brainstorm several methods you could use to test your hypothesis given the materials provided. As a group, select one method for your experimental design. 2. Identify the independent, dependent, and controlled variables, and the type of data you will collect. 3. As you prepare your procedure, be sure to consider the time required for each step. 4. Prepare the data table you will use to record your observations. Decide what form (such as the type of graph) you will use to present your results. 5. Review your procedure with your teacher. Do not begin doing the investigation until your teacher has approved your group s procedure. 6. Record your observations in your table. Make notes about any findings that do not fit in your data table. Record any questions that come up as you conduct your investigation. Analyze and Interpret 1. Did your observations support or refute your hypothesis? Explain. 2. Did your investigation allow you to draw conclusions about the inheritance of the genes that are involved in the production of chlorophyll? Why or why not? 3. Identify the variables you considered when designing your investigation. Explain why you needed to consider each variable to obtain scientifically valid results. Conclude and Communicate 4. State your conclusions about the relationship between exposure to light and the activity of the genes that are involved in the production of chlorophyll. Extend Further 5. INQUIRY Could a different hypothesis be consistent with the results of your investigation? How could you design an investigation to test this different hypothesis? 6. RESEARCH What social benefit could come from understanding the effect of light on chlorophyll production? Chapter 6 Complex Patterns of Inheritance MHR 269

31 ThoughtLab INVESTIGATION 6-B Skill Check Initiating and Planning Performing and Recording Analyzing and Interpreting Communicating Materials data on crosses Sex-linked Crosses Thomas Morgan used Drosophila melanogaster, the common fruit fly, extensively in his studies of sex-linked traits. In this investigation, you will model Morgan s experiments using Drosophila melanogaster and use your results to confirm sex-linked inheritance for the trait you chose to study. Pre-Lab Questions 1. How is a sex-linked recessive trait distinguished from an autosomal recessive trait? 2. Describe the genotype of the P generation that could be used to model Morgan s studies of sex-linked genes in Drosophila. 3. What phenotype is expected in the F 1 generation produced from the cross described in question 2? Question How are sex-linked traits inherited in Drosophila melanogaster? How do actual results compare with theoretical ratios? Organize the Data 1. Choose one trait from the table below (eye colour, eye shape, or body colour) to investigate. Go to Organizing Data in a Table in Appendix A for help with designing a table for data. Common Sex-linked Traits in Drosophila melanogaster Trait Phenotype 1 Phenotype 2 Eye colour White Red Eye shape Round Bar Body colour Black Yellow A B Two forms of eye colour in fruit flies are white and red (A). Eye shape can be round (A) or appear as narrow bars (B). 270 MHR Unit 2 Genetic Processes

32 Part I: The F 1 Generation 2. Determine the genotype of the flies use for the P generation. 3. Construct a table to record your results. 4. Use a computer simulation program or obtain results for the F 1 generation from your teacher. Record the results in your table. 5. Before beginning Part II, complete the Analysis section of the investigation for Part I. Part II: The F 2 Generation 6. Determine the genotype of the flies for the F 1 cross. 7. Construct a table to record your results. 8. Use a computer simulation program or obtain results for the F 2 generation from your teacher. Record the results in your table. Analyze and Interpret Part I 1. From the data you recorded on the appearance of the flies in the F 1 generation, which trait is dominant? Explain your answer. 2. Given your response to question 1, form a hypothesis about the phenotypic ratio that you will observe in the F 2 generation. Conclude and Communicate 4. Describe the inheritance pattern for the trait you studied in this investigation. 5. How does the actual phenotypic ratio you obtained compare to the theoretical phenotypic ratio? Account for any differences. Extend Further 6. INQUIRY In this investigation, you tracked the inheritance pattern of one sex-linked trait. Design an investigation that would track the inheritance of one of these traits and the autosomal trait of normal versus vestigial wings. Describe the results you expect. 7. RESEARCH Drosophila melanogaster has been used extensively in genetics research. What other traits have been studied in Drosophila? On which chromosomes are the genes for these traits located? Part II 3. Calculate an actual phenotypic ratio of the F 2 generation from your results. A B Two forms of body colour in fruit flies are black (A) and yellow (B). Chapter 6 Complex Patterns of Inheritance MHR 271

33 Chapter 6 SUMMARY Section 6.1 Beyond Mendel s Observations of Inheritance Some patterns of inheritance are more complex than those first proposed by Mendel. These include codominant and incomplete dominant inheritance patterns. In addition, for some traits multiple alleles for a gene can exist within the population. KEY TERMS codominance continuous variation heterozygous advantage incomplete dominance polygenic trait KEY CONCEPTS Incomplete dominance leads to the expression of an intermediate phenotype. In the case of codominance, both alleles are fully expressed. Although an individual has only two alleles for any gene, multiple alleles for a gene may exist within the population. Environmental conditions can influence the expression of certain traits. Polygenic traits are controlled by more than one gene and can usually be identified by continuous variation in phenotype. Section 6.2 Inheritance of Linked Genes Some traits are inherited together, due to linked genes. Gene linkage includes sex-linked genes, which are on the sex chromosomes. KEY TERMS linked genes sex-linked trait KEY CONCEPTS Alleles of different genes that are on the same chromosome do not assort independently. These genes are said to be linked and their associated traits tend to be inherited together. Sex-linked traits are expressed in different ratios by male and female offspring because they are determined by the segregation of X and Y chromosomes. Although sex-linked genes are linked to the X and Y chromosomes, Punnett squares can be used to predict genotypes and phenotypes. Section 6.3 The Future of Genetics Research Current and future research in genetics involves studying how phenotypes result from complex interactions between genes and gene products. KEY TERMS bioinformatics genetic profile genomics KEY CONCEPTS The complete DNA sequence of the human genome was determined as part of the Human Genome Project. The field of bioinformatics arose from the need to share and maintain the large quantities of data collected from genomic research. It also provides tools for analyzing genomic data. There is still much to be learned from the data generated from the Human Genome Project, particularly in identifying genes that are associated with human health. Current and future research in genomics may allow scientists to tailor preventative and curative treatments for individual patients based on their specific genetic profiles. However, ethical questions about who owns an individual s genetic information continue to be debated. 272 MHR Unit 2 Genetic Processes

34 Chapter 6 REVIEW Knowledge and Understanding Select the letter of the best answer below. 1. The seed colour of a particular species of plant is inherited through incomplete dominance. If a true-breeding plant with blue seeds is crossed with a true-breeding plant with yellow seeds, what is the expected seed colour of the offspring? a. yellow b. green c. blue d. yellow and blue spots e. You cannot predict seed colour from the information given. 2. Roan cows are the result of a codominant inheritance pattern. In roan cows, the allele for white hair and the allele for red hair are both expressed. Which of the following is the most appropriate representation for codominant alleles? a. Let W = allele for white hair, and let R = allele for red hair. b. Let W = allele for white hair, and let r = allele for red hair. c. Let w = allele for white hair, and let R = allele for red hair. d. Let C W = allele for white hair, and let C R = allele for red hair. e. Let C w = allele for white hair, and let C R = allele for red hair. 3. A man with blood type O and a woman with blood type AB have a child. Which of the following are possible blood type(s) for the child? a. O only b. AB only c. A or B d. A, B, or O e. A, B, AB, or O 4. Skin colour in humans ranges from very dark to very light. Which of the following most likely describes how skin colour is inherited? a. principle of dominance b. incomplete dominance c. codominance d. polygenic inheritance e. environmental influence 5. The following pedigree follows the inheritance pattern of sickle cell anemia in a family. What is the sex, genotype, and phenotype of individual II-5? I II III a. unaffected female, Hb A Hb S b. affected female, Hb A Hb S c. unaffected male, Hb S Hb S d. affected male, Hb S Hb S e. unaffected male, Hb A Hb A 6. An X-linked dominant allele is inherited from a heterozygous female by a. all of her sons b. half of her sons c. all of her daughters d. none of her daughters e. all of her children 7. Which of the following most accurately describes the field of genomics? a. the study of haplotypes b. the study of how DNA is copied c. the study of how genes interact to produce a phenotype d. the study of how genomes are formed e. the study of the inheritance pattern of genes 8. How has DNA microarray technology revolutionized the study of gene activity? a. Gene expression in cells can now be studied. b. The proteins produced by genes have been discovered. c. Many genes can be studied at the same time. d. The human genome has been completely sequenced. e. All of the proteins produced in a cell can now be studied. 2 5 Chapter 6 Complex Patterns of Inheritance MHR 273

35 Chapter 6 REVIEW Answer the questions below. 9. A plant that produces white flowers is crossed with a plant that produces red flowers. Describe the pattern of inheritance if the flowers produced are a. pink b. red and white spotted c. all red 10. What is the predicted phenotypic ratio in the F 2 generation if two alleles are inherited by incomplete dominance? 11. What is heterozygous advantage? Provide an example. 12. Describe how multiple alleles influence inheritance of a trait. Provide an example. 13. Height is an example of a polygenic trait. What aspect of height suggests this? 14. What are linked genes? Explain why their inheritance is not according to the law of independent assortment. 15. Parents who do not have symptoms of Duchenne muscular dystrophy have a son with Duchenne muscular dystrophy. Which parent has passed the disease to their son? Explain your answer. 16. What is a person s genetic profile? What are some ethical issues concerning access to this information? Thinking and Investigation 17. A man with straight hair has two children with a woman who has curly hair. One child has straight hair, and one has wavy hair. What pattern of inheritance for hair type does this suggest? 18. Use the pedigree below to answer the following questions. The letters in the symbols indicate the blood type of each individual. a. Determine the blood types of individuals I-4 and I-6. b. Individual III-2 and a man with blood type AB have four children. Will any of these children have blood type O? Explain. I II III A AB B? O? 1 AB 1 B A AB O O O A B A O In foxes, a pair of alleles, C P and C p, interact as follows: C P C P is lethal, usually during an embryonic stage C P C p produces platinum-coloured fur C p C p produces silver foxes. Could a fox breeder establish a true-breeding variety of platinum foxes? Explain. 20. A man with type B blood and a woman with type AB blood have children. What blood types are possible among their children? What would tell you that the man is heterozygous for type B blood? 21. A woman with type AB blood has a child with the same blood type. What are the possible genotypes of the father? 22. What could be a genetic reason for the black area of fur forming after a cold pack has been placed on the back of this Himalayan rabbit? 23. Explain why genes that are far apart on a single chromosome may be inherited as though they are on different chromosomes. 24. A horse breeder finds that one of his stallions has a genetic defect that affects the production of sperm. The gene associated with this trait is located on the Y chromosome. What is the possibility that the stallion s female offspring could pass on this trait to their sons? Explain. 25. Fruit flies can have normal wings or stunted wings. In an investigation, you mate several normal-winged females with a male that has stunted wings. In the F 1 generations, only the males have stunted wings. What can you conclude from this investigation? 26. Suppose that the first dihybrid crosses Mendel performed had involved traits controlled by closely linked genes. a. How would Mendel s results have differed from the results he obtained for a dihybrid cross involving non-linked genes? b. What hypothesis might Mendel have developed to explain his results? c. What investigation could Mendel have conducted to test this hypothesis? What would he have observed? 274 MHR Unit 2 Genetic Processes

36 Communication 27. Rudy and Maria are expecting a baby. They have normal vision, but both of their fathers are colour vision deficient (CVD). Their mothers have normal vision. a. Draw a pedigree for their family. b. What is the probability that the baby will be a girl with CVD? c. What is the probability that the baby will be a boy with normal vision? 28. The closer genes are together on a chromosome, the more likely they will assort together. Illustrate this concept with a model or diagram. 29. Variability and diversity of living organisms result from the distribution of genetic materials during the process of meiosis. Mendel proposed the idea that all genes assort independently, producing offspring with a variety of traits whose distribution can be predicted mathematically. William Bateson and Reginald Punnett found that not all genes do assort independently. Develop a diagram that shows independent assortment and how linked genes contradict this theory. 30. Genetic and genomic research can have social and environmental implications. Identify a potential scientific outcome of genomics research. Develop an illustration showing the possible social implications of achieving that outcome. 31. In this chapter, DNA sequences in a genome are compared to letters strung together in a book. Develop another analogy for DNA, chromosomes, genes, and nucleotides. Illustrate your analogy with a diagram or model. 32. Use a graphic organizer to summarize the uses of bioinformatics in genetics research. 33. There are many benefits to genetics research, but there are also significant ethical concerns. Use a concept map to illustrate some of the benefits and concerns that are associated with the different genetics research topics discussed in this chapter. 34. Summarize your learning in this chapter using a graphic organizer. To help you, the Chapter 6 Summary lists the Key Terms and Key Concepts. Refer to Using Graphic Organizers in Appendix A to help you decide which graphic organizer to use. Application 35. A farmer wants to breed a variety of taller corn. a. How can the farmer use variation in the height of the current corn plants to produce taller corn plants? b. Will the farmer s work be most effective if height in corn plants is determined by polygenic inheritance, multiple alleles, or codominant alleles? Explain. c. The farmer finds that many of the tallest corn plants are also very susceptible to a particular disease. How could the farmer design an investigation to find out if the genes for height are linked to the genes that cause susceptibility to the disease? d. If these genes are linked, what steps could the farmer take to create a breed of corn that is taller and more disease-resistant than the current corn crop? 36. Figure 6.17 provides a summary of some important discoveries in genetics research, including the Human Genome Project. a. Research one development or discovery that is in the figure, including an aspect of the Human Genome Project. Choose a subject that you have not learned about in this unit. b. As part of your research, find out about at least one individual who is associated with the discovery or invention. c. Summarize your findings and develop a presentation that you could present to the class or another general audience. Make sure your presentation includes a discussion on the importance of the discovery in terms of its contribution to scientific research. 37. Genome Canada was established in 2000 to develop a national program for financial support of genomic and proteomic research in Canada. a. Choose a research project that is funded by Genome Canada and that is listed on the Genome Canada website. b. Write a brief description that summarizes what the project is studying. Include the names of the individuals associated with the project and at what institution(s) they work. c. Research Genome Canada s GE 3 LS program. What does this acronym stand for and what are the main objectives of this program? Develop an argument for or against the importance of having such a program. Chapter 6 Complex Patterns of Inheritance MHR 275

37 Chapter 6 SELF-ASSESSMENT Select the letter of the best answer below. 1. K/U Incomplete dominance occurs when a. one allele masks the expression of the other allele b. one trait is masked by the presence of another trait c. both alleles are expressed when the alleles occur together d. an intermediate phenotype is expressed when the alleles occur together e. an unpredictable phenotype is expressed when the alleles occur together 2. K/U Which of the following is an example of codominance? a. A plant with green seeds is crossed with a plant with white seeds; the offspring produce white seeds. b. Individuals who are heterozygous for sickle cell disease produce both normal and sickle-shaped red blood cells. c. A red snapdragon crossed with a white snapdragon produces pink snapdragons. d. There are many genes that control eye colour. e. A litter of kittens often display a wide variety of traits. 3. T/I A man who is homozygous for blood type A and a woman who is homozygous for blood type B have a child. Which of the following could be the child s genotype? a. I A i b. I A I A c. I B i d. I B I B e. I A I B 4. K/U Which two terms are most relevant to the inheritance of human blood types? a. incomplete dominance and codominance b. codominance and multiple alleles c. incomplete dominance and multiple alleles d. codominance and polygenic inheritance e. dominance and codominance 5. K/U Traits that exhibit continuous variation are usually a. controlled by one gene b. the result of codominance c. dominant d. polygenic e. affected by the environment Use the following information to answer questions 6 and 7. The gene that controls coat colour in rabbits has four alleles: agouti (C), chinchilla (c ch ), Himalayan (c h ), and albino (c). The order of dominance is C > c ch > c h > c. 6. K/U What is the phenotype of a rabbit with the genotype c ch c? a. agouti b. chinchilla c. chinchilla and albino mix d. Himalayan e. albino 7. T/I If a rabbit with the phenotype c ch c h is crossed with an albino rabbit, what is the probability of producing a Himalayan rabbit? a. 0 percent b. 25 percent c. 50 percent d. 75 percent e. 100 percent 8. K/U How can linked genes become unlinked? a. During meiosis, they sort independently. b. During crossing over, they are separated. c. During anaphase, they segregate to opposite poles in the cell. d. During mutation, the genes are separated. e. During DNA replication, the genes are rearranged. 9. T/I Hemophilia is an X-linked recessive disorder. If a female with hemophilia and a male without hemophilia had children, what is the predicted percentage of children who would have hemophilia? a. 0 percent b. 25 percent c. 50 percent d. 75 percent e. 100 percent 10. K/U Which of the following statements about the Human Genome Project is false? a. It involved sequencing the human genome. b. It identified coding and non-coding sections of DNA. c. It involved sequencing the genome of common representative organisms. d. It identified genes in the human genome. e. It determined the functions of the genes in the human genome. 276 MHR Unit 2 Genetic Processes

38 Use sentences and diagrams as appropriate to answer the questions below. 11. T/I In radishes, colour is controlled by two alleles, one for red colour and one for white colour. Inheritance of these alleles shows incomplete dominance. The photographs below show the phenotype for each possible colour: red, purple, and white. What phenotypic ratio would you expect from crossing two heterozygous radish plants? 12. T/I A student crosses a true-breeding plant that produces green seeds with a true-breeding plant that produces yellow seeds. Predict the possible offspring when a. the allele for green seeds is dominant to the allele for yellow seeds b. the allele for green seeds is codominant with the allele for yellow seeds c. the alleles for green and yellow seeds are incompletely dominant 13. C Blood type ABO is determined by three alleles. Draw a diagram that shows how blood type is determined by a combination of the three alleles. 14. A Investigating environmental effects on gene expression is an important aspect of genetics research on plant crops. Explain why, using an example of a trait to illustrate your answer. 15. C Draw a diagram that illustrates the concept of linked alleles of genes. In your diagram, show how they can become unlinked. 16. C A female fruit fly that is homozygous dominant for red eyes is crossed with a white-eyed male fruit fly. Use a Punnett square to predict the genotype(s) and phenotype(s) of their offspring. 17. T/I The pedigree below illustrates the sex-linked inheritance pattern of a trait in a family. I II III a. Explain how this pedigree shows sex-linked inheritance. What type of sex-linked inheritance is it? Explain. b. From the pattern of inheritance you determined in part (a), determine the genotype of II-2. c. Based on your answer to part (a), determine the probability that individuals II-1 and II-2 would have an affected child. 18. C Duchenne muscular dystrophy affects many more males than females. Explain why and draw a pedigree to illustrate its inheritance pattern. 19. K/U Explain why males cannot be carriers of an X-linked trait. 20. K/U Explain how Barr bodies account for the patchy colours of female calico cats. 21. K/U Why did the Human Genome Project include the sequencing of other organisms? 22. C Decoding the human genome can be compared to reading a book in a language that nobody knows or understands. Explain this statement using diagrams or a graphic organizer. 23. A What is genomics research? How can it be used to improve human health? 24. A What is bioinformatics? Describe a scientific study that uses bioinformatics. 25. A The human genome has long stretches of DNA that do not code for proteins. Describe how the variation between individuals in these regions can be useful to study. Self-Check If you missed question... Review section(s) Chapter 6 Complex Patterns of Inheritance MHR 277

39 Unit 2 Project An Issue to Analyze Analyzing the Risks and Benefits of GMOs For many years farmers have used reproductive technologies such as selective breeding to produce the strongest and most profitable plants and animals possible. Now genetic engineering allows scientists to manipulate genomes. All of the organisms shown below have been genetically modified to become transgenic organisms. Recall that a genetically modified organism, or GMO, is one whose genome has been altered. A transgenic organism is produced when this alteration involves the insertion of a gene from another organism. The merits of producing such organisms are continually debated. The long-term effects that GMOs have on humans who are exposed to them, on the modified organisms themselves, and on the environment are not yet known. Assume the role of a science writer who contributes to an on-line magazine that is a forum for discussions on the impact of GMOs on society. Choose a GMO and research its application(s). Analyze the benefits and risks associated with the use of this organism and develop recommendations regarding its application(s). What are the issues related to the use of genetically modified organisms, and do the benefits outweigh the possible risks? Initiate and Plan 1. Select one GMO and its application(s). Some options for you to consider are organisms genetically modified to be more resistant to disease organisms genetically modified to improve medical treatment for humans (for example, plants or animals used in pharmaceutical production) organisms genetically modified to be more resistant to very cold temperatures organisms genetically modified to provide alternative and/or higher yield food products for human consumption organisms genetically modified to allow for easier harvesting organisms genetically modified to improve environmental conditions Most canola plants grown in western Canada have had a bacterial gene inserted into their genomes that makes them resistant to herbicides. 278 MHR Unit 2 Genetic Processes This Enviropig has had a bacterial gene inserted into its genome that enables it to break down a phosphorus-containing compound in feed. These GloFish have had a gene from sea anemones inserted into their genomes that makes them glow in the dark.

40 Perform and Record 2. Research your chosen GMO. Focus your initial research on the scientific technology associated with the development of the organism, and on the regulatory processes that must be followed. 3. Consider the following questions to guide your research: What type of genetic modification have scientists made to the organism? Does this modification involve inserting a gene from another organism, to produce a transgenic organism? What government regulatory bodies are involved in reviewing the research, development, and use of the organism (for example, local municipal government, provincial government, Health Canada, Environment Canada, U.S. Food and Drug Administration)? At what stage of research and development is the genetic engineering of the organism and its application(s)? Is research still at a preliminary stage? Has research and development received some kind of government approval? Has the organism or its products received government approval for commercial use? 4. Research the economic, political, societal, ethical, and environmental issues related to the application(s) of the GMO that you have selected. 5. Consider the following questions to guide your research: Who stands to benefit the most from the application(s)? What is the most significant benefit? What is the most significant risk to the environment (if any), and to society as a whole? What, if any, long-term benefits and risks have citizens or scientists identified regarding the use of this GMO? What are the sources of the information you have gathered? How trustworthy and credible are your sources? How do you know? Analyze and Interpret 1. Prepare a risk-benefit analysis that outlines the risks and benefits associated with the development of the GMO and its application(s). Refer to Analyzing STSE Issues in Appendix A for help with how to do this analysis. 2. Make recommendations about whether development and use of the GMO should continue as is, should stop, or requires stricter regulations. Support your recommendations using specific examples from your risk-benefit analysis. Communicate Your Findings 3. Choose a form of communication to convey your recommendations that is appropriate for an on-line magazine (such as a web page, blog, podcast, or Internet video). Assessment Criteria Once you complete your project, ask yourself these questions. Did you K/U select an appropriate GMO? K/U describe the scientific and technical principles related to the technology and the regulatory processes that must be followed? A identify the economic, political, societal, ethical, and environmental issues related to the technology? A make recommendations based on specific examples from the risk-benefit analysis of whether use of the GMO should continue as is, be stopped, or be under stricter regulations? C organize your research using an appropriate format and appropriate academic documentation? C select a format for your recommendations that is appropriate for the audience and purpose? C use scientific vocabulary appropriately? Unit 2 Project MHR 279

41 UNIT 2 SUMMARY Genetic and genomic research can have social and environmental implications. Variability and diversity of living organisms result from the distribution of genetic materials during the process of meiosis. Overall Expectations In this unit you learned how to evaluate the importance of some recent contributions to our knowledge of genetic processes, and analyze social and ethical implications of genetic and genomic research investigate genetic processes, including those that occur during meiosis, and analyze data to solve basic genetic problems involving monohybrid and dihybrid crosses demonstrate an understanding of concepts, processes, and technologies related to the transmission of hereditary characteristics Chapter 4 Cell Division and Reproduction KEY IDEAS Chromosomes in human somatic cells are organized into 23 pairs. One pair is the sex chromosomes, and the other 22 pairs are the autosomes. Meiosis produces haploid gametes from diploid parent cells. It leads to genetic variation in gametes through the independent assortment of chromosomes and crossing over of genetic material. Errors during meiosis can result in changes to the structure and number of chromosomes. Modern technologies allow scientists to manipulate the genetic make-up of organisms. This has led to many benefits. Chapter 5 Patterns of Inheritance KEY IDEAS Mendel s monohybrid and dihybrid cross experiments demonstrated the existence of dominant and recessive forms of traits. The combination of alleles in an individual is its genotype. The expression of the genotype in an individual is the phenotype. A dominant phenotype is expressed when a dominant allele is present. A recessive phenotype requires two copies of the recessive allele. Punnett squares are used to study the genotypes and phenotypes of offspring. Pedigrees provide information about the inheritance of genotypes and phenotypes of individuals across generations within a family. Karyotyping, fluorescence in situ hybridization (FISH), and gene testing are used to monitor chromosome structure, chromosome number, and disease-causing genes. Chapter 6 Complex Patterns of Inheritance KEY IDEAS Some patterns of inheritance are more complex than those first proposed by Mendel. These include codominant and incomplete dominant inheritance patterns. In addition, for some traits multiple alleles of a gene exist in the population. Linked genes occur on the same chromosome and tend to be inherited together. However, crossing over can unlink these genes. Sex-linked traits are expressed in different ratios by male and female offspring because they are governed by the segregation of X and Y chromosomes. The Human Genome Project determined the complete DNA sequence of the human genome. Many new research fields and methods have developed from this project. Current and future research in genomics may allow scientists to tailor medical treatments for individual patients based on their genetic profiles. However, ethical questions about who owns genetic information continue to be debated. 280 MHR Unit 2 Genetic Processes

42 UNIT 2 REVIEW Knowledge and Understanding Select the letter of the best answer below. 1. Which phase of meiosis is shown in the illustration below? 5. Which of the following statements best describes an individual whose genetic make-up is shown below? a. prophase I b. prophase II c. metaphase I d. metaphase II e. interphase 2. Which of the following statements best describes the difference between a daughter cell produced by mitosis and one produced by meiosis? a. A cell produced by mitosis is genetically identical to a cell produced by meiosis. b. A cell produced by mitosis has half the DNA content of a cell produced by meiosis. c. A cell produced by meiosis has half the DNA content of a cell produced by mitosis. d. A cell produced by mitosis is genetically altered due to crossing over, but a cell produced by meiosis is not. e. A cell produced by mitosis can produce an egg or sperm cell, but a cell produced by meiosis cannot. 3. Which of the following processes contributes to genetic variation? a. cloning b. mitosis c. crossing over d. interphase e. cytokinesis 4. A cross is performed between two pea plants, one with the genotype Tt, and the other with the genotype tt. If 250 offspring are produced, approximately how many have the genotype Tt? a. 0 b. 63 c. 125 d. 180 e. 250 a. The individual is a male with the correct number of chromosomes. b. The individual is a female with the correct number of chromosomes. c. The individual is a male with trisomy. d. The individual is a female with trisomy. e. The individual is a female with monosomy. 6. Blue flowers (B) is dominant to white flowers (b). A true-breeding plant with blue flowers is crossed with a true-breeding plant with white flowers. Which of the following statements represents a result of this cross? a. The offspring all have the genotype Bb. b. The offspring are all homozygous recessive for blue flowers. c. The offspring are all homozygous recessive for white flowers. d. The offspring all have the phenotype bb. e. The offspring are all homozygous dominant for blue flowers. 7. What is the predicted phenotypic ratio of the offspring from a dihybrid cross between two individuals that are heterozygous for both traits? Assume that the two genes involved are not linked. a. 3:1 b. 9:3:3:1 c. 1:2:2:1 d. 1:1:1:1 e. 1:3 Unit 2 Review MHR 281

43 UNIT 2 REVIEW 8. What is a key indicator of autosomal dominant inheritance? a. The trait is passed from father to son. b. The trait is passed from father through an unaffected daughter to her sons. c. The trait skips generations. d. Two unaffected parents have an affected child. e. Two affected parents have an unaffected child. 9. Incomplete dominance is expected when a. one allele prevents the expression of the other allele b. the expression of one allele is masked by the presence of another allele c. an intermediate phenotype is expressed when the alleles occur together d. both phenotypes are expressed when the alleles occur together e. the phenotypes are expressed randomly when the alleles occur together 10. A man with blood type AB married a woman with blood type B who carries an allele for blood type O. What are the possible blood types of their children? a. O b. A and B c. A and AB d. B and AB e. A, B, and AB Answer the questions below. 11. What happens during each phase of interphase? 12. What is a karyotype and what is it used for? 13. What are the important features that make chromosomes homologous pairs? Why are homologous chromosomes not identical? 14. What are haploid and diploid cells? Where is each cell type found? 15. What are the two essential outcomes of meiosis? Identify the phases of meiosis where these outcomes are achieved. 16. The diploid cells of a fruit fly (Drosophila melanogaster) contain four chromosomes. a. How many pairs of chromosomes does a diploid cell of a fruit fly contain? b. How many chromosomes does a haploid cell of a fruit fly contain? c. How many genetically distinct gametes can be produced from a parent? 17. Mendel performed his ground-breaking genetic experiments using pea plants. List three characteristics of pea plants that helped Mendel obtain such conclusive results, and thus allowed him to develop his theory of inheritance. 18. Describe what the terms dominant and recessive mean. How are they used to describe the forms of a trait at the genotype level and at the phenotype level? 19. What are monohybrid and dihybrid crosses? How can Punnett squares be used to represent these crosses? 20. What is meant by the phrase autosomal recessive inheritance? In your explanation, use an example of a genetic disorder that is inherited in this manner. 21. Describe the chromosome theory of inheritance and the contribution that Walter Sutton s research made to the development of this theory. 22. Describe three types of genetic tests that are done and the information that each provides. 23. Why is sickle cell anemia an example of codominant inheritance? 24. Explain how a single gene may have multiple alleles. Include an example of a trait affected by multiple alleles in your explanation, and describe how multiple alleles affect phenotypes. 25. Colour vision deficiency (CVD) is a sex-linked trait. Explain why males cannot be carriers for CVD. 26. Describe the role that bioinformatics played in the Human Genome Project. 27. Describe the similarities and differences between mitosis and meiosis. 28. What is the difference between a gene and an allele? Thinking and Investigation 29. Errors can occur during meiosis that result in alterations to the number and structure of chromosomes. a. Describe the different types of errors. b. What methods are used to detect and differentiate between these errors? 30. How do artificial insemination and embryo transfer differ in terms of controlling genetic variation? 31. Compare and contrast oogenesis and spermatogenesis. List their similarities and their differences. 282 MHR Unit 2 Genetic Processes

44 32. If black coat colour is dominant to white coat colour in an animal, what is the a. genotype of a homozygous black-coated animal? b. genotype of a homozygous white-coated animal? c. genotype of a heterozygous animal? d. genotypes of the gametes produced by each of the animals in parts (a) to (c)? 33. The following data were obtained from an initial cross between a true-breeding round-seeded pea plant and a true-breeding wrinkled-seeded pea plant. a. Based on the data, what are the dominant and recessive forms of seed shape? Explain your answer. b. Do the data in the tables support the Mendelian ratio? Explain your answer, and any differences observed. Results for the F 1 Generation Trait Form Number of Offspring Plants with round seeds 175 Plants with wrinkled seeds 0 Results for the F 2 Generation Trait Form Number of Offspring Plants with round seeds 154 Plants with wrinkled seeds In humans, the allele for peaked hairline is dominant to the allele for smooth hairline. Is it possible for two adults with peaked hairlines to have a child with a smooth hairline? Explain. 35. Copy and complete the table below in your notebook, given the information about pea plants in Table 5.1 and the following: T = tall plant G = green pod colour Y = yellow seed colour Gamete from Male Parent TY Gt Yg Gamete from Female Parent ty gt yg Genotype of Offspring Phenotype of Offspring 36. In pea plants, the allele for purple flowers is dominant to the allele for white flowers and the allele for tall plants is dominant to the allele for short plants. Two pea plants that are heterozygous for both traits are crossed, producing 272 offspring. a. Provide the genotype of each parent. b. What are the genotypes of the gametes from each parent? c. What is the expected number of offspring that are short plants with white flowers? 37. The pedigree below traces a genetic disorder in a family. I II a. Do you think the disorder has an autosomal dominant or autosomal recessive inheritance pattern? Why? b. Provide the genotypes and phenotypes for all individuals in this pedigree. Explain your answer. If there is a genotype you cannot be sure of, explain why. 38. In snapdragons, the alleles for flower colour display incomplete dominance. a. A red-flowered plant is crossed with a white-flowered plant. What are the predicted genotypes and phenotypes of the offspring? Explain your answer. b. An offspring produced from the mating in part (a) is crossed with a white-coloured snapdragon. What are the predicted phenotypes and genotypes of the offspring? Include the phenotypic ratio of the offspring. 39. From the following blood types, determine which baby belongs to which parents. Explain your answer. Baby 1 blood type O Baby 2 blood type B Mr. Jones blood type A Mrs. Jones blood type A Mr. Guttierez blood type A Mrs. Guttierez blood type AB 40. Determine the probability of a hemophiliac child being born when neither the father nor the mother has hemophilia, but the mother s father has hemophilia. Is there any chance that their daughters will be affected? Why or why not? 41. How do epigenetics and genetics differ? Provide two examples of investigations that illustrate the differences between these fields of study. Communication 42. Draw an illustration that shows the relationship between DNA, chromatin fibre, a chromosome, a gene, an allele, and homologous chromosomes. Unit 2 Review MHR 283

45 UNIT 2 REVIEW 43. Summarize the process of meiosis in graphic form, illustrating the movement and number of chromosomes in each cell. 44. Variability and diversity of living organisms result from the distribution of genetic materials during the process of meiosis. Crossing over and independent assortment play an important role in genetic recombination. Draw labelled diagrams to show how they provide genetic variation. 45. Genetic and genomic research can have social and environmental implications. Through genetic modification, some crop plants can be engineered to be more resistant to disease. Many organizations and citizen groups oppose the use of these crops. Choose a crop plant that has been genetically modified to be more resistant to disease. Research the risks and benefits associated with this technology. Illustrate these benefits and risks in a pamphlet, poster, or graphic organizer. 46. Use a diagram to illustrate how transgenic organisms are created. 47. A Punnett square can be used to predict the possible outcomes of a genetic cross. Explain graphically how a Punnett square uses the laws of probability by diagramming a cross between two pea plants heterozygous for height (given that the allele for tall plants is dominant to the allele for short plants). Predict the genotypic and phenotypic ratios for the offspring based on the results of your Punnett square. 48. Using Punnett squares, illustrate how someone could determine whether an organism with a dominant phenotype is heterozygous for that trait. 49. Assume you write a monthly blog for an on-line magazine that provides information to the general public about various genetic disorders. You have been asked to write about Huntington disease. a. Provide a description of the genetic abnormality that causes Huntington disease and the inheritance pattern of the disorder. Also include a brief statement about the symptoms, diagnosis, and treatment options that are available. b. Write a brief paragraph describing your opinion on whether genetic testing for Huntington disease should be mandatory for family members when there is a family history of the disorder. Include valid points to support your argument. 50. Draw a diagram that illustrates gene linkage. 51. Since Mendel performed his experiments with pea plants, scientists have discovered that there are more complex patterns of inheritance. Use examples and diagrams to illustrate the differences among the following mechanisms: dominance incomplete dominance codominance sex-linked inheritance 52. Draw a pedigree that could represent the inheritance of hemophilia in a family. When drawing the pedigree, ensure that you choose genotypes that will clearly illustrate the pattern of inheritance for hemophilia. Provide a brief rationale for why the pedigree shows the correct inheritance pattern. 53. In this unit, you have learned how different fields of study are applied to provide a better understanding of genetic processes and human disease. For example, bioinformatics was essential for the success of the Human Genome Project. Develop an illustration using one or two examples of different fields of study or technologies that have worked together to provide a more complete understanding of a genetic process. Application 54. Type 1 diabetes is managed effectively with synthetic insulin produced by bacteria. Why do scientists continue to research this disease in hopes of finding other treatments or a cure? 55. What is the risk of relying on artificial insemination or embryo transfer to produce the offspring in a herd of animals? 56. Stem cell research has led to many ground-breaking discoveries, as well as thought-provoking controversies. a. Describe some of the controversy surrounding stem cell research and how new research has managed to reduce the controversy. b. Research a development in regenerative medicine that has come from stem cell research in Canada. Describe what the research involved, as well as its potential benefit to society. 57. Scientists believe that most human diseases involve a complex array of interactions between genetic and environmental factors. Why is it not possible to follow a trait such as high blood pressure by performing a monohybrid cross, as done by Mendel with pea plants? Be sure to include both scientific and ethical considerations in your answer. 284 MHR Unit 2 Genetic Processes

46 58. Many breeds of dogs are known for a high incidence of genetic disorders. German shepherd and Saint Bernard dogs, like the one shown below, are predisposed to developing a crippling condition called hip dysplasia. a. Why are purebred dogs more at risk for such conditions than mixed breeds? b. What advice would you give to dog breeders who want to maintain their dogs purebred pedigrees, but also want their dogs to be as healthy as possible? 61. Many organisms undergo a heat shock response when they are placed at higher temperatures than they normally live at. One part of this response involves increased expression of certain genes, which helps the organisms to cope with the higher temperature. a. Describe a technique that could be used to monitor this response in an organism. b. Saccharomyces cerevisiea, shown below, is a type of yeast that undergoes a heat shock response. This organism has been extensively used in genetics studies. Research the use of Saccharomyces cerevisiea in genetics studies. Provide a summary of why it is such a useful organism for this type of research. 59. Cystic fibrosis is a genetic disorder that leads to the build-up of thickened mucus in the lungs and other organs. Individuals affected by cystic fibrosis are more susceptible to respiratory illnesses and must undergo physical therapy regularly to manage the symptoms of the disease. a. Describe the genetic basis of cystic fibrosis and its pattern of inheritance. b. How can a genetic counsellor help affected individuals and their families? c. One hope for a cure for cystic fibrosis is gene therapy. Describe how gene therapy could be used to cure cystic fibrosis, and the obstacles that must be overcome for gene therapy to provide that cure. 60. Develop a plot for a movie or play that involves the use of gene therapy. Ensure that the application is accurate scientifically. 62. Bioinformatics has applications in many fields of study. a. Research how bioinformatics is playing an important role in cancer research. b. Identify a research group in Canada that is using bioinformatics as part of its studies in cancer research. c. Summarize the information you gather and present your findings to the class, using a format of your choice. 63. How can having your genetic profile determined pose both potential risks and benefits? How has this development of genetics research brought to light the need for new social and political policies? 64. Our knowledge in the areas of genetics and genomics has grown incredibly since Choosing one specific example, discuss how this research has increased our understanding of human health and disease. Unit 2 Review MHR 285