Winnie s Study Guides: Adv. Biology. Chapter 14: Mendel and the Gene Idea Page

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1 [Adv. Bio] Ch14-1 Winnie s Study Guides: Adv. Biology Chapter 14: Mendel and the Gene Idea Page Overview: Drawing from the Deck of Genes In the 1800s, people generally believed the blending hypothesis o Genetic material contributed by two parents mixed to create the child Ex. My black hair + my future British husband s blonde hair = dark yellow/gold/orange hair for my daughter<3 o Failed to explain why traits sometimes skipped a generation An alternative to the blending model is the particulate hypothesis of inheritance o The gene idea o Parents pass on discrete heritable units (genes) that retain their separate identities in offspring o Like playing cards (hah get the title?) the genes are shuffled and passed along from generation after generation By the way, that s Gregor Mendel! 14.1 Mendel used the scientific approach to identify two laws of inheritance Mendel breeded garden peas in carefully planned experiments Mendel s Experimental, Quantitative Approach o His beautiful childhood Grew up on parents small farm in a region of Austria (current Czech Republic) so he received agricultural training in school

[Adv. Bio] Ch14-2 Overcame financial hardship and illness to excel in high school and later at the Olmutz Philosophical Institute (woo inspiration for us BCA kids.

2 [Adv. Bio] Ch14-2 Overcame financial hardship and illness to excel in high school and later at the Olmutz Philosophical Institute (woo inspiration for us BCA kids..) Joined a monastery at age 21, tried to become a teacher but failed the examination. Left monastery to study physics and chemistry at the University of Vienna. This was important because Professor (and physicist) Christian Doppler encouraged his students to learn science through experimentation and trained Mendel to use math to help explain natural phenomena Professor Franz Unger (and botanist) got Mendel to like plants Returned to monastery to teach at a local school and began his garden pea plant journey o Benefits of working with pea plants Many varieties purple/white flowers, numerous characters Character a heritable feature that varies among individuals o Ex. Color of flowers Trait each variant for a character o Ex. Purple or white Short generation time Large number of offspring from each mating Mendel could strictly control it o In nature, pea plants self fertilize. (Pollen grains from stamens land on carpel sperm from pollen grains fertilize eggs present in the carpel) o To prevent this, Mendel cut off the immature stamens from a plant (See picture on ) o Mendel s Gardening Methods Chose to track characters that occurred in two distinct, alternative forms Practiced true-breeding True-breeding breeding pea plant so that over many generations of self-pollination, only the same variety as the parent plant is produced o Basically, he kept breeding the same plant over and over again til he was sure only purple flowers would appear. Cross-pollinated two different types of peas Hybridization mating or crossing of two true-breeding varieties P generation parental generation (true-breeding parents) F 1 generation first filial generation (offspring of P) o Filial means son in Latin F 2 generation second filial generation MENDEL WAS UNIQUE BECAUSE he bred plants past the F1 generation. Most botanists before stopped after F1 The Law of Segregation

3 [Adv. Bio] Ch14-3 o P generation = white and purple true breeds F1 generation = all purple F2 generation = white and purple?! WHY o Mendel kept large sample sizes and accurate records o F2: 705 purple plants and 224 white plants o Mendel defined a dominant trait and a recessive trait o Repeated this experiment with other characteristics in flowers o Law of Segregation: The two coexisting alleles of an individual for each trait segregate (separate) during gamete formation so that each gamete gets only one of the two alleles. Alleles again unite at random fertilization of gametes. Mendel s Model o Four concepts that make up the 3:1 inheritance pattern 1. Alternative versions of genes account for variations in inherited characters Alleles alternative versions of a gene 2. For each character, an organism inherits two copies of a gene, one from each parent 3. If the two alleles at a locus differ, then one, the dominant allele, determines the organism s appearance; the other, the recessive allele, has no noticeable effect on the organism s appearance Dominant allele allele that will overshadow the recessive allele; determines the organism s appearance Recessive allele the allele that is not dominant; aka it needs two of them to show up 4. The Law of Segregation: the two alleles for a heritable character segregate (separate from each other) during gamete formation and end up in different gametes BASICALLY, if I have a trait for blonde hair (I wish) and a trait for black hair, I can only give one of them to my baby o This is where there were about two super long paragraphs describing a punnett square in words. This is a punnett square. (See right) I clearly remember learning this in 5 th grade. You should all know what a punnett square is. I am not going to outline those two obnoxiously long paragraphs. Punnett square a handy diagrammatic device for predicting the allele composition of offspring from a cross between individuals of known genetic makeup Useful Genetic Vocabulary o Homozygous having a pair of identical alleles for a character Ex. PP or pp Will breed true o Heterozygous having two different alleles for a gene Ex. Pp Will not breed true-breeding gametes o Phenotype an organism s appearance or observable traits o Genotype genetic makeup The Test Cross

[Adv. Bio] Ch14-4 o You have a mystery pea plant that is purple o To determine the genotype, cross the plant with a white-flowered palnt (pp) o If all the flowers are purple, the mystery pea plant

4 [Adv. Bio] Ch14-4 o You have a mystery pea plant that is purple o To determine the genotype, cross the plant with a white-flowered palnt (pp) o If all the flowers are purple, the mystery pea plant was a PP. If there are a few white flowers, then the mystery pea plant was a Pp o Testcross breeding an organism of unknown genotype with a recessive homozygote The Law of Independent Assortment o Mendel had originally just looked at color in his first experiment Monohybrids heterozygous for one particular character being followed in the cross Monohybrid cross cross between such heterozygotes BASICALLY, it only focused on one characteristic o Mendel discovered his second law by studying seed color and seed shape at the same time Y=yellow; y=green R=round; r=wrinkled YYRR and yyrr P generation will produce dihybrids in the F1 generation dihybrids F 1 individuals heterozygous for the two characters being followed in the cross dihybrid cross a cross between F 1 dihybrids Question that Mendel asked: Does YR stay together and does yr stay together? NO Mendel found out by using this huge Punnett square (see below) It resulted in a 9:3:3:1 ratio

5 [Adv. Bio] Ch14-5 o Law of Independent Assortment: each pair of alleles segregates indepdently of each other pair of alleles during gamete formation Only applies to genes (allele pairs) located on different chromosomes Chromosomes that are not homologous or very far apart on the same chromosome 14.2 The laws of probability govern Mendelian inheritance The Multiplication and Addition Rules Applied to Monohybrid Crosses o Multiplication rule to determine the probability of specific combinations, you must multiply the probability of one event by the probability of the other event LOL WE LEARNED THIS AT MATH TEAM<3 Basically, ½ chance of landing on heads. You want the probability of landing on it twice. (½)(½)=1/4 o Can be applied to monohybrids ½ chance of receiving dominant allele and ½ chance of receiving recessive allele from another plant.. ¼ chance of receiving both of them o Addition rule the probability that any one of two or more mutually exclusive events will occur is calculated by adding their individual probabilities Mutually exclusive two events that are different but can be combined together Ex. Flower one can give either the R or the r gene. Another flower can give either the R or the r gene. These are two exclusive events because the events don t affect each other, but they are still mutual because they eventually combine to find the final probability Solving Complex Genetics Problems with the Rules of Probability o There is about a page of explaining how to calculate probability in biology. If you re on math team, you should be fine. If you re not, I would read the chapter OR DO THIS: o Draw a punnett square! o All the annoying really long math here is essentially calculating the probability for only the necessary squares in the huge punnett square. I personally think drawing the punnett square and counting the boxes that match the criteria is easier Inheritance patterns are often more complex than predicted by simple Mendelian genetics Mendel focused on traits that were triggered by only one gene. Now we will go deeper into this topic by looking at super complicated ways of how other traits work! Yay! (It s late, and I m really tired, lol.) Extending Mendelian Genetics for a Single Gene o Sometimes genes have more than two alleles o Sometimes a single gene produces multiple phenotypes Degrees of Dominance

6 [Adv. Bio] Ch14-6 o Alleles can show different degrees of dominance and recessiveness in relation to each other o Complete dominance the situation in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable Ex. Mendel s purple/white pea plants o Incomplete dominance the situation in which the phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele Ex. White snapdragon + red snapdragon = pink snapdragon o Codominance the situation in which the phenotypes of both alleles are exhibited in the heterozygote because both alleles affect the phenotype in separate, distinguishable ways Ex. some people may have the M allele (MM) for red blood cells, and some people may have the N allele (NN) for red blood cells. The MM allele causes M molecules on red blood cells. The NN allele causes N molecules on red blood cells. Some people have NM. This makes them have both N and M molecules on their red blood cells. o The Relationship Between Dominance and Phenotype Dominant allele does not interact with recessive allele BUT THEIR PATHWAYS INTERSECT Ex. wrinkled vs. round seeds Round seeds are caused by the dominant round allele which codes for an enzyme that helps convert an unbranched form of starch into a branched form within the seed. Wrinkled seeds are caused by the recessive wrinkled allele coding for a defective form of this enzyme. Thus, there is a lot of unbranched starch which causes excess water to enter the seed by osmosis. Later, the seed dries and the seed wrinkles The dominant allele just makes sure that there is enough good enzymes Ex. Tay-Sachs disease Brain cells of a child with Tay-Sachs disease cannot metabolize certain lipids because a crucial enzyme does not work properly. Lipids accumulate in brain cells and child begins to suffer seizures, blindness, and degeneration of motor and mental performance and dies within a few years Two copies of Tay-Sachs allele disease (thus it is recessive) Only one copy of Tay-Sachs allele no disease (the one non- Tay-Sachs allele was enough to produce enough enzymes to metabolize lipids THUS, THE NORMAL AND TAY-SACHS ALLELES ARE CODOMINANT. THEY ARE BOTH WORKING. o Frequency of Dominant Alleles Dominant alleles aren t always the most prevalent in society Polydactyly (having extra fingers or toes) is caused by a dominant gene. Not many people have it though. (I don t have it! :D)

[Adv. Bio] Ch14-7 Multiple Alleles o Pea plants that Mendel studied only two alleles existed o However, most traits are determined by three alleles Ex.

Pleiotropy o Does each gene only affect one phenotypic character? NOOOOOOOOOOOOOOOOOOO!!! o Most genes are pleiotropic o Pleiotropy having multiple phenotypic effects Ex.

7 [Adv. Bio] Ch14-7 Multiple Alleles o Pea plants that Mendel studied only two alleles existed o However, most traits are determined by three alleles Ex. Blood groups There are three alleles: I A, I B, and i. Thus, people may have either type A, B, AB, or O blood. See diagram on the left! Pleiotropy o Does each gene only affect one phenotypic character? NOOOOOOOOOOOOOOOOOOO!!! o Most genes are pleiotropic o Pleiotropy having multiple phenotypic effects Ex. In pea plants, the gene that determines flower color also affects the color of the coating on the outer surface of the seed Extending Mendelian genetics for Two or More Genes o What happens when two or more genes are involved in determining a particular phenotype? o Epistasis Epistasis is Greek for standing upon Epistasis phenotypic expression of a gene at one locus altering that of a gene at a second locus BASICALLY, a gene at one part of the chromosome affecting a gene at some other location Ex. Labradors (aww<3) Black coats are dominant to brown. (black=b; brown=b) Thus, brown fur=bb and black fur=bb or BB However, a second gene decides whether the pigment will be put in the fur (gene E) o E=pigment deposited o e=pigment not deposited Thus, BbEe BLACK DOG! o bbee BROWN DOG! o Bbee YELLOW DOG! o bbee YELLOW DOG! See chart on side for more details o Polygenic Inheritance Mendel only studied things that could be classified on an either-or basis Ex. Purple or white However, human skin color and height are DIFFERENT! They are quantitative characters

8 [Adv. Bio] Ch14-8 Quantitative characters a heritable feature that varies continuously over a range rather than in an either-or fashion This indicated polygenic inheritance Polygenic inheritance an additive effect of two or more genes on a single phenotypic character Ex. Skin pigmentation in humans is controlled by at least three separately inherited genes Genes = A, a, B, b, C, c (capitals representing darker skin tone) AABBCC very super dark skin AaBbCc medium tone skin aabbcc extremely pale AaBbcc between pale and medium ETC!!! Nature and Nurture: The Environmental Impact on Phenotype o Phenotype for a character also depends on environment besides just genotype o Ex. A tree with tall genes will grow taller than a tree with the same genotype if the first tree has more sunlight, water, happy tree! (Jk, I won t personify trees you shouldn t either lol) o Hotly debated: whether human traits are more affected by nature or nurture o Thus, phenotype is a RANGE OF PHENOTYPIC POSSIBILITIES Ex. My parents are short. My doctor says I will be between 5 2 and 5 4. Why? If I drink milk (lol idk if that s a myth), I will grow taller. If I don t, I will stay at Nature is my genotype that makes me 5 2 through 5 4. Nurture is whether I drink milk to make myself taller. o Norm of reaction The range of phenotypes produced by a single genotype, due to environmental influences Aka just a fancy name for phenotypic range o Thus, due to norm reaction, there are traits that are affected by genotypes and outside conditions. There genes are called multifactorial. o Multifactorial having many factors, both genetic and environmental, collectively influence phenotype Integrating a Mendelian view of Heredity and Variation o (This is pretty much a conclusion of 14.3) o Degrees of dominance are generally decided by multiple alleles, pleiotropy, epistasis, polygenic inheritance, and the phenotypic impact of the environment o We should try to understand things as a whole Look at phenotype as the entire organism Look at genotype as the entire genome o Wow Mendel was so amazing! 14.4 (Many human traits follow Mendelian patterns of inheritance) Many Mendelian patterns of inheritance o Humans are more difficult to study than pea plants because we cannot be forced to mate, our lifespans are longer, and we have few offspring. o Pedigree Analysis Rather than manipulating mating patterns of people, geneticists can analyze results of matings

9 [Adv. Bio] Ch14-9 Collect family s history for a trait and assemble information on a family tree FAMILY PEDIGREE! Pedigree A diagram of a family tree with conventional symbols, showing the occurrence of heritable characters in parents and offspring over multiple generations Important application: to calculate the probability that a future child will have a particular genotype and phenotype Recessively Inherited Disorders o Thousands of genetic disorders exist o The Behavior of Recessive Alleles Genes code for proteins of specific function Recessive gene, a, causes a genetic disorder by coding for a malfunctioning protein or no protein at all Thus, Aa = no disorder, AA = no disorder, but aa = disorder Genetic disorders only show up with homozygous individuals, not heterozygous ones Heterozygotes can transmit recessive allele to offspring; they are carriers Carriers - In genetics, an individual who is heterozygous at a given genetic locus for a recessively inherited disorder. The heterozygote is generally phenotypically normal for the disorder but can pass on the recessive allele to offspring. Genetic disorders are not evenly distributed among all groups of people Tay-Sachs disease is disproportionately high among Ashkenazi Jews (Jewish people whose ancestors lived in central Europe) o This is because people were geographically isolated and bred with each other Consanguineous ( same blood ) matings mating with someone that is closely related to you o Cystic Fibrosis Most common lethal disease in the United States (1 out of every 2,500 people) 1 out of every 25 people of European descent are carriers for this allele Normal allele codes for a membrane protein that functions in the transport of chloride ions between certain cells and the extracellular fluid Chloride transport channels are defective or absent in the plasma membranes of children who inherit two recessive alleles for cystic fibrosis abnormally high concentration of extracellular chloride which means mucus coats certain cells to become stickier and thicker mucus builds up and essentially the patient drowns in his/her mucus o Sickle-Cell Disease: A Genetic Disorder with Evolutionary Implications

10 [Adv. Bio] Ch14-10 Most common inherited disorder among people of African descent (1 out of every 400) Caused by substitution of a single amino acid in the hemoglobin protein in red blood cells oxygen content of an affected individual s blood is low sickle-cell hemoglobin molecules aggregate into long rods that deform the red cells into a sickle shape clogs arteries and may cause stroke/heart attacks Codominant alleles so even if you are heterozygous for the trait, you will show characteristics of it but not as extreme Explanation of this disease in evolution: having a single copy of sicklecell allele reduces frequency and severity of malaria attacks Dominantly Inherited Disorders o There are some human disorders caused by dominant alleles Ex. Achondroplasia dwarfism (1 in every 25,000 people) Recessive allele is much more prevalent than the corresponding dominant allele o Dominant alleles that cause a lethal disease are much less common than recessive alleles that have lethal effects Arise by mutations in cells that produce sperm or eggs Usually not passed on to future generations because it kills the individual before he/she can mature and reproduce o Huntington s Disease: A Late-Onset Lethal Disease Timing is important because an allele can be passed if it causes death at a relatively advanced age Huntington s disease A human genetic disease caused by a dominant allele; characterized by uncontrollable body movements and degeneration of the nervous system; usually fatal 10 to 20 years after the onset of symptoms 1 in 10,000 people Fortunately, we can now analyze a person s genome to test for the Huntington s allele Multifactorial Disorders o Previous diseases were caused by an abnormality of one or both alleles at a single genetic locus o However, there are diseases that have a multifactorial basis o Multifactorial basis a genetic component plus a significant environmental influence o Examples: <3 disease, diabetes, cancer, etc. o Thus, lifestyle does have a tremendous effect on the phenotypes of disorders Genetic Testing and Counseling o Avoiding simple Mendelian disorders is possible if the risk of a genetic disorder is assessed before a child is conceived o Counseling Based on Mendelian Genetics and Probability Rules Hypothetical couple: Bob and Jen

11 [Adv. Bio] Ch14-11 Bob s brother has a genetic disorder. Jen s brother has a genetic disorder. ½ chance each of them are carriers. ¼ chance for them to give it to their child. o Tests for Identifying Carriers Tests are available for some disorders to distinguish individuals of normal phenotype who are dominant homozygotes from those who are heterozygous carriers Enable people with family histories of genetic disorders to make informed decisions about having children People cannot be denied health or life insurance nor can they lose their jobs through these tests by the Genetic Information Nondiscrimination Act of o Fetal Testing If you ever conceieve a baby and realize you and your wife/hubby are carries for a genetic disorder, you can always try these! Amniocentesis - A technique associated with prenatal diagnosis in which amniotic fluid is obtained by aspiration from a needle inserted into the uterus. The fluid and the fetal cells it contains are analyzed to detect certain genetic and congenital defects in the fetus. Chorionic villus sampling (CVS) - A technique associated with prenatal diagnosis in which a small sample of the fetal portion of the placenta is removed for analysis to detect certain genetic and congenital defects in the fetus. Also, you may be able to obtain fetal cells/dna that have escaped into the mother s blood Other methods that can t really diagnose a genetic disorder but are commonly used: Ultrasound reflects sound waves to created an image Fetoscopy a needle-thin tube containing a viewing scope and fiber optics inserted into the uterus for viewing o Newborn Screening Simple biochemical tests routinely performed in hospitals after birth Testing for PKU (phenykletonuria) Recessively inherited disorder Children cannot metabolize phenylpyruvate which can accumulate to toxic levels in the blood Activity Summary Concept 14.1 o There is an 8 minute MP3 tutor that will teach you the chromosomal basis of inheritance o There is an activity to teach you about a monohybrid cross with alien eyes o There is an activity to teach you about a dihybrid cross with alien eyes AND skin o There is a LabBench that guides you through a lab about flies/genders/hairs It ll take you around 20 minutes to go through it and understand it

12 [Adv. Bio] Ch14-12 o Biology Labs On-Line is not available to us Concept 14.2 o There is an activity (more like a video) that lets you work alongside Mendel in his garden it s cute looool Concept 14.3 o There is an activity to teach you about a incomplete dominance with alien horns Concept 14.4 o There is a 2 minute discovery channel video to talk about novelty genes Talks about how risk-takers may have a gene that releases more dopamine making risk-takers want to take more challenges for more dopamine BTDUBS, dopamine is a chemical signal in the body that influences people to have more pleasure yay o There is an investigation How Do You Diagnose a Genetic Disorder? it will take you around 10 minutes to go through the beginning video of the grandma scared me

Chapter 14. Mendel and the Gene Idea

Chapter 14. Mendel and the Gene Idea Chapter 14 Mendel and the Gene Idea Gregor Mendel Gregor Mendel documented a particular mechanism for inheritance. Mendel developed his theory of inheritance several decades before chromosomes were observed