Nucleic Acids Nucleic acids are one of the 4 major found in all living things. A macromolecule is also known as a, which means it is a molecule made of smaller repeating known as. The monomers of nucleic acids are called. There are two major classes of nucleic acids: 1) DEOXYRIBONUCLEIC ACID (DNA) DNA is the chemical basis for the, the fundamental unit of and is responsible for governing the of the entire cell. DNA is mainly found in the of cells but is also present in the. 2) RIBONUCLEIC ACID (RNA) RNA molecules are mainly found in the of cells and perform, such as acting as structural scaffolds or being chemical messengers. There are a variety of different forms of RNA including,,, and. Nucleotides: A nucleotide consists of three parts: i) A nitrogenous base (so called because nitrogen atoms form part of the rings of the molecule) There are two types of nitrogenous bases, and. In DNA, there are two purine bases, and and two pyrimidine bases, and that are used to make nucleotides. In RNA, adenine, guanine and cytosine occur, but does not, it is replaced by the pyrimidine.
Pyrimidines (single ring) Purines (double ring) ii) A 5-carbon sugar (in DNA it is ; in RNA it is ) iii) A phosphate group
A nucleic acid polymer consists of alternating chains of and, with a nitrogenous base attached to a deoxyribose (or ribose) sugar. The nucleotide is held together by bonds that are known as a. A molecule of RNA is a structure that often becomes, while DNA takes on, formation. In DNA, bonds are formed between nitrogenous base pairs and are held together through bonding. The nitrogenous base pairs between the DNA double helix always pair up such that and are together and and are joined.
Nucleotides are not only important as building blocks of nucleic acids; they also have important functions in their own right. Most of the energy being put to use at any given moment in any living organism is derived from the nucleotide (ATP).
Genes and Chromosomes Deciphering the Genetic Code The is the major functional sub-unit of DNA. Genes are specific sequences of that have the potential to be and to an organism s. We often think of genes as the portion of information that defines one particular trait of an organism s physical characteristics. The sum of the entire including all of the ( - ) within a cell is referred to as the. The specific, and of genes are unique to each species, but even organisms that are only may carry very similar genes. In humans genes are organized onto. Each chromosome contains linear double-stranded molecules. DNA molecules are held together with called. A chromosome is actually protein, DNA, RNA. Genes are along chromosomes. The density of genes can vary from one chromosome to another. For example, in humans: Chromosome 4 Chromosome 19 There is no set relationship between the number of genes on a chromosome and the total length of the chromosome
Central Dogma DNA provides the information that ultimately codes for a specific to be produced. This is a two-step process of, followed by. Transcription is a process that occurs within the, where the information from one gene is used as a to produce a strand of nucleotides (mrna) that is then moved into the. Translation is the process where the mrna transcript is used to generate a sequence of, which will eventually fold into a threedimensional structure and become an active protein. This process occurs in the of cells and requires a number of ( and ). Information for the genetic code is read as a series of consecutive or. Each codon ultimately corresponds to a specific that will be added to a growing chain.
Mutations A mutation is any type of genetic change. There are several types of mutations, some which go ; others are, while others still may have serious, effects. The following are common mutations that can occur during replication: Base Substitution A different is substituted. Examples: Silent - Mis-sense Non-sense - Frameshift mutation Addition or deletion of a can throw off Example: SEETHEREDCATANDTHEFATDOG SEEHEREDCATANDTHEFATDOG Even without exposure to, each of your genes undergoes of mutations during your life; most of these are corrected by.
Cell Division You are made up of approximately cells. This is amazing considering that all these cells started from one fertilized egg. Even now cells are dividing in your body! Cell division is needed for: 1. Growth - 2. Repair - 3. Reproduction How does cell division occur? Cell division occurs in three stages: 1. Replication The replication process must be relatively and it must be for cells to survive. Remarkably, cells are able to duplicate their DNA in a few, with an error rate of approximately per nucleotide pair! 2. Mitosis - 3. Cytokinesis - The end result of these stages are from one original cell.
In order to describe the events of the cell cycle, the process has been divided into several phases: INTERPHASE: The cell is doing its in the form of cannot be seen Cell At the end of interphase the DNA has PROPHASE: disappears disappears DNA and and becomes visible - form and can be seen move apart METAPHASE: Chromosomes line up at of cell Centrioles are located at Spindle fibres attach to and centrioles
ANAPHASE: Centromeres and singlestranded move to opposite poles Pulled by spindle fibres TELOPHASE: Opposite of reappears reappears disappears Chromatid become and and cannot be seen ( ) FINAL RESULT OF CELL DIVISION: occurs (division of cytoplasm) Two cells
Meiosis Different characteristics are displayed by different people. This variation in characteristics is shown because each person comes from a different family. Even within a family there are differences. Each human cell has chromosomes in total or of chromosomes. Each pair of chromosomes resembles each other in, and. You receive one member of each pair from your and the other from your. These pairs of chromosomes are called. Your genes are located on these chromosomes. Meiosis is the process by which a cell (2n) produces (n) gametes or sex cells. Meiosis occurs only in the of most living things: Spermatogenesis = Oogenesis = Plants =
Meiosis Terminology Diploid Two sets of (2n) Body cells ( ) are diploid cells Human cells have chromosomes or 2 sets (2n) of chromosomes Haploid Single set of (n) Sperm or egg ( ) are haploid cells Human sex cells have chromosomes Homologous chromosomes (homologues) Two chromosomes similar in and that carry the genetic information Inherit one chromosome from each Zygote The cell that results when an and a unite ( ) Synapsis The pairing of chromosomes Occurs in of meiosis Tetrad Two homologous chromosomes form a loose connection of Crossing over The process where the ends of chromosomes (adjacent) become or together and The ends of the homologous chromosomes may or places Explains why all offspring will be (except identical twins) Non-disjunction During meiosis one chromosome does not get to the proper end of the cell One cell may get chromosomes and others too few
Stages of Meiosis (Interphase occurred first) Phase Diagram Key events Prophase I Same as prophase of mitosis and disappear become visible (previously ) appear occurs as homologous chromosomes pair up The of information occurs in a process called Metaphase I line up at the of the cell Chromosomes align randomly and differently each time through meiosis (law of ) Anaphase I Tetrads and double stranded chromosomes move to the of the cell Telophase I Two cells forming, with the number of chromosomes Each strand is because of crossing over Chromosomes still must be separated into single stranded chromatid
Prophase II Same as mitosis prophase Metaphase II Double stranded chromosomes line up at the Same as mitosis metaphase Anaphase II Double stranded chromosomes into single stranded Same as mitosis anaphase Telophase II Four cells with the number of chromosomes Each cell is genetically different from each other and different every time meiosis occurs
Early Ideas About Genetics Mendelian Genetics Aristotle (384-322 BC) Pangenesis - every part of the body was involved in the production of the seeds of the parents; seeds fused to give rise to a new individual. Anton van Leeuwenhoek (1632-1723) The idea of an animalcules in the semen of males a tiny preformed embryo. 19th Century Blending theory of inheritance Charles Darwin Offspring had variations of their parent's characteristics; but he could not explain why. Gregor Mendel (1822-1884) Developed the fundamental principles that became the modern science of genetics. Mendel s Experiments Gregor Mendel was a monk, whose studies included mathematics and botany. He conducted a series of experiments on pea plants over an eight-year period. Mendel used bred (or breeding) pea plants for his experiments, which are plants that produced (Example - tall or short). Mendel actually studied different traits, each trait that had only possible variations. Mendel obtained pure bred plants through. Useful terminology: P generation = F1 generation = F2 generation =
Mendel bred pure breeding tall plants with pure breeding short plants. All of the offspring were tall. The tall pea plants were then crossed with each other. The resulting offspring showed a 3:1 ratio of tall plants to short plants. These results led Mendel to conclude that the trait for plants must be and the trait for plants to be. When both a dominant and a recessive trait are present, only the one will itself. Mendel conducted theses experiments many times, using the seven different traits. For each test, he obtained the same results. In addition, Mendel came up with the : i) The inherited traits (or ) are determined by pairs of factors or. ii) The alleles segregate (or ) in the formation of (eggs or sperm) iii) The alleles are one from each parent.
Using the information obtained from Mendel s experiments, we can look at his experiments again from the point of view that every trait is associated with a different allele. Symbols are assigned to the alleles. Capital letters for dominant traits and lower case for recessive. Examples: T = tall and t = short The are the alleles for a particular trait. The is how the alleles physically manifest themselves. Genotypes can be either homozygous or heterozygous. means that both of the alleles are the (TT or tt). means the two alleles are (Tt).
Punnett Squares Comparing one trait at a time in breeding experiment is referred to as a monohybrid cross. The results can be organized in a Punnett square; a way of calculating the probability of inheriting a particular trait. It is a simple method of illustrating all possible combinations of gametes from a given set of parents. Examples: In guinea pigs, black fur is dominant to white fur. What would the F2 generation look like if you started with a male homozygous for white fur and a female homozygous for black fur? Cross a white furred male with a female from the F1 generation.
Test Cross A test cross is a type of breeding experiment that can be used if the of an organism is, but the is. The test cross is always performed between the organism with an unknown genotype (that carries a dominant allele or ) and an organism that has a genotype. A test cross would NOT be employed to determine human genotypes. Sample Problem: Having blue flowers is dominant (B) is a dominant characteristic to the recessive trait of having pink flowers (b). By performing a test cross with an plant of unknown genotype that has blue flowers, determine the possible outcomes that could result. When performing a test cross there are only two possible outcomes that can occur: 1. offspring will appear to have the trait. This would suggest that the unknown organism has a genotype that is. 2. the offspring would have the trait and would have the trait. This would suggest that the unknown organism has a genotype that must be. Test crosses have proven to be a useful tool in the process of. Selective breeding is the crossing of traits from plants or animals to produce that have one or several of the desired characteristics.
Selective breeding commonly employs the techniques of either or. is the mating of to produce offspring with desirable characteristics of parents. is the process by which mating occurs between for the purpose of certain characteristics. Inbreeding can often result in manifesting themselves. Practice Questions If you are given a dominant round (R) seed pea plant and you need to know the genotype of this plant, you need to do a test cross. What pea plant genotype would you cross this mystery dominant plant with? In doing this cross, you find that the offspring are all round. What does this indicate about the mystery parent genotype? In doing this cross, you find that the offspring show a 1:1 ratio of round:wrinkled. What does this indicate about the mystery parent genotype? In corn, the allele for purple kernels is dominant to the alleles for yellow kernels. Determine the likely genotypes of the parents if the offspring that results from pollination produce 47 purple kernel producing plants and 14 yellow kernel producing plants. This idea of using the phenotypes of offspring to predict the genotypes of parents is employed when studying human inheritance patterns. This is called.
Pedigree Analysis Pedigree chart: From the point of view of individual III - 1, the symbols represent the following relationships: I - 1 = I - 2 = II - 1 and II - 2 = II - 3 = II - 4 = II - 5 =
III - 2 = III - 3 = Practice Problem #1 The following Pedigree shows a family with the trait of shortsightedness. The allele for shortsightedness (E) is dominant to the allele for normal vision (e). Predict the genotypes for each individual in the family. Practice Problem #2 Phenylketonuria (PKU) is a genetic disorder caused by a dominant allele. People with PKU are unable to metabolize a naturally occurring amino acid, phenylalanine. If phenylalanine accumulates it inhibits the development of the nervous system, leading to mental retardation. The symptoms of PKU are not evident at birth, but can develop quickly if the child is not placed on a special diet. The pedigree chart below shows the inheritance of the defective allele in one family. a) How many generations are shown in the pedigree? b) How many children were born to the parents of the first generation? c) What are the genotypes of individuals 1 and 2 in generation I? d) How is it possible that in generation II, some of the children showed symptoms of PKU, while others did not?
e) Individuals 6 and 7 in generation II had a child without PKU. Does this mean that they can never have a child with PKU? Explain your answer. Incomplete Dominance and Codominance Not all alleles interact under the principle of dominance and recessive. Incomplete dominance is when both alleles contribute to the of the organism, creating a in a genotype. Example: In four o'clock flowers, red flowers (C R ) is incompletely dominant to white (C W ). The heterozygous plants (C R C W ) are pink in colour. What are the possibilities for the F2 generation starting with a cross between a red and white flower? Codominance: Two dominant alleles are expressed at the.. Example: In cattle, red hide colour (R) is codominant to white (W). Cows that are heterozygous for this trait have a roan hide colour (RW), where the red hair and white hair both appear on the animal. Cross two roan cows and determine the chance of getting a white animal. Sometimes it is a benefit for an individual to inherit two different alleles for the same trait. This is called. An example is a person who is heterozygous for the sickle cell gene; they have some normal red blood cells and are resistant to.
Dihybrid Crosses 1. What is the frequency of tossing one dice and having it roll the number one? 2. What is the frequency of tossing two dice and having both roll one? 3. What is the frequency of tossing a Yahtzee! Five dice that all roll the number one? The above examples illustrate that the result of one toss of the dice has no affect on the outcome of future rolls, that is, one s dice action is segregated from the others and independent. In his studies Gregor Mendel discovered that like the dice, alleles assort independently from each other. Mendel termed this,. The law states that: This simply means that the inheritance of alleles for one characteristic does not affect the inheritance of alleles for another characteristic (as long as the alleles are on different chromosomes). Example: Whether a human has attached or free earlobes has no effect upon whether or not their hair is curly or straight. The characteristics are independent from one another. Mendel came up with the idea for the law of independent assortment while studying the inheritance of in crossbreeding (following the same procedures he had used for studying single traits). This kind of approach is called a. There are two approaches we can take to determine the probability for each of the possible outcomes to occur in a dihybrid cross.
Approach #1 You can solve a dihybrid problem by completing two separate monohybrid crosses, one for each of the characteristics being examined. Then the crosses can be combined to calculate the probabilities of the dihybrid crosses. Example: In garden pea plants the pod colour green (G) is dominant over the recessive allele yellow (g); while round seed shape (R) is dominant over wrinkled (r). Following mating between parents with the genotypes GgRr x GgRr, what are the probabilities of obtaining offspring with the following characteristics: Green pods and round seeds Yellow pods and round seeds Green pods and wrinkled seeds Yellow pods and wrinkled seeds Pod Colour Probability Seed Shape Probability Combined Probability Green Round Yellow Round Green Wrinkled Yellow Wrinkled
Approach #2 The alternative method to solving dihybrid problems has you come up with all the possible combinations of alleles that can occur during a cross, and then completing a giant Punnett square. The first step is to identify the complete genotype of each organism in the cross (this will include 4 alleles, two for each trait being examined). Using the previous example of green (G) and yellow (g) pea pods and round (R) and wrinkled (r) pea seeds : What is the probability of obtaining a green and wrinkled peas? Predict the chance of a yellow and round pea from the following parents: ggrr x Ggrr
Multiple Alleles Many traits in humans and other species are the result of the inheritance of more than two alleles for one gene. A gene with more than two alleles is said to have. Blood Types In humans a single gene determines a person's ABO blood type. This gene determines what type of an, if any, is attached to the cell membrane of red blood cells. An antigen protein is a molecule that stimulates the body's. The gene is designated " " and it has three common alleles:, and. The different combinations of the three alleles produce the four different phenotypes of blood. A & B are dominant to O. A & B are codominant. The possible genotypes for blood typing are: I A I A - I B I B - I A i - I B i - I A I B - ii - Examples: A man with hybrid type A blood and a woman with type AB blood wish to know the possible blood types for their children.
A rich couple are confronted by a man who claims to be the man's son from a previous marriage. The son's blood type is "O" and both the man and his ex-wife are hybrid type A. What is the probability that the young man is telling the truth? Rh Factor In addition to the substances that cause A, B, and O blood types there is another factor called the Rh factor that can be found in blood. The genes for having the Rh factor are completely dominant to the genes for not having the Rh factor. For example: Let: R - have the Rh factor r - absence of the Rh factor Therefore, RR and Rr produce people that are Rh positive & rr only produce an Rh negative individual. What are the possibilities for a man that is pure type B and pure Rh positive with a woman who is hybrid A and Rh negative? In addition to the many traits being controlled by one gene with multiple alleles, there are also many traits that are, which means they are controlled by gene. Examples of polygenic traits include, height, skin colour and eye colour. These traits tend to exhibit in which the phenotype varies gradually from one extreme to another.
Sex Linkage Linked genes are genes that are on the and that tend to be. These genes DO NOT exhibit Mendel's law of independent assortment and therefore do not follow the Mendelian inheritance patterns that have been previously discussed. Sex Determination Human cells contain chromosomes ( pairs). The first pairs are referred to as ; these chromosomes carry the. Your 23 rd pair of chromosomes are called your chromosomes; these are the ones that determines your sex, but they also carry. Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX). Sex Linkage Thomas Hunt Morgan (1866-1945) was an American geneticist who worked with fruit flies (Drosophila melanogaster) and developed theories on and. Fruit flies are an ideal subject for study in genetics because: They reproduce rapidly Offspring can mate shortly after leaving the egg Females produce over 100 eggs each mating You can study many generations in a short period of time They are small can be housed in a single culture tube Males can be easily distinguished from females. Morgan s Experiment
Morgan explained his experiments by concluding that the X and Y chromosomes contain different genes, and that in his fruit flies, the Y chromosome does not carry the gene to determine eye colour. Morgan called characteristics that are controlled by genes located on the sex chromosomes as. In humans there are numerous sex-linked traits: Males and females produce the same amount of coded by located on the X chromosome. However, females have two copies of this chromosome while males only have one. Experiments have shown that one of the X chromosomes in each female cell is. Which one is inactivated is, and therefore different X chromosomes are active in different cells. The inactivated X chromosome is called a. Sex-Linked Problems What are the possible offspring for a cross between a normal female and a colour-blind male? Let: X - Normal gene for colour-vision male X c - Recessive gene for colour-blindness In humans, baldness is sex-linked and recessive to normal amount of hair. For hair colour, black is incompletely dominant to blonde, heterozygous have brown hair colour. Show the possible offspring for a man who is bald and had brown hair and a woman who is blonde and a carrier for baldness.