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# GEN Study Guides 1 & 2 Bio 2450

Texas State

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This 7 page Study Guide was uploaded by Ashton Willey on Tuesday September 20, 2016. The Study Guide belongs to Bio 2450 at Texas State University taught by Dr. Nice in Fall 2016. Since its upload, it has received 9 views.

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Date Created: 09/20/16

Study Guide and Additional Problems 1 Study Questions: 1. Define these terms: true-breeding, dominant, recessive, monohybrid cross, gene, allele, homozygous, heterozygous, genotype, phenotype, segregation, parental, F , F , st nd 1 2 Mendel’s 1 law, Mendel’s 2 law, dihybrid cross, Punnett square, testcross, branch diagram, backcross, probability, Chi-square, degrees of freedom, multiplicative rule, additive rule, binomial probability, Pascal’s triangle, sex determination, aneuploidy, X-linkage, Y-linkage, nondisjunction. 2. What problems did the concept of blending inheritance create for the Darwin’s and Wallace’s theory of evolution by natural selection? 3. In your opinion, what was unique and/or different about Mendel’s experiments, results and hypothesis. 4. Explain Mendel’s hypothesis and his two laws. 5. How did Mendel’s hypothesis revolutionize the study of inheritance? 6. Assume that Mendel’s hypothesis predicting a 3:1 ratio in the F gene2ation is correct for a trait under study. Explain how the value of the Chi-square statistic changes as the number of offspring in the F i2creases. 7. Explain how dominant traits can be detected from pedigree analysis. Explain how recessive traits differ from dominant traits. Explain how sex-linked traits can be detected from pedigree analysis. 8. Explain the functional differences between mitosis and meiosis. How does the behavior of the chromosomes differ and what is the significance of these differences? 9. Explain how Morgan’s and Bridge’s work with Drosophila provided support for the chromosome theory of inheritance. Recommended problems from chapter 11: 11.1 – 11, 15-20, 22-27, 32, 33, 35 Recommended problems from chapter 12: 12.1, 3-6, 8, 11-19, 22-34, 42, 43, 46, 47 Additional Problems: 1. One of Mendel’s first experiments involved crosses between true-breeding lines of peas with inflated pods and peas with pinched pods. In the F gen1ration, all plants had inflated pods. A. Diagram Mendel’s experiment. What would the F generati2n look like? Include the genotype and phenotype of all individuals involved. B. If an F individual was backcrossed to the pinched pod parental line, what 1 genotypes could be produced? C. Draw a branch diagram of the original experiment. D. Draw a branch diagram of the backcross described in B. 2. Imagine a large grocery bag filled randomly with donuts. 2/3 of the donuts are chocolate, the rest are coconut. A small boy is reaching into the bag to get some donuts for his brothers and sisters. A. What is the probability that the boy pulls out a coconut donut? B. What is the probability that the boy pulls out two chocolate donuts? C. What is the probability that boy pulls out two donuts and one is chocolate and one is coconut? D. The boy’s sister wants a coconut donut. The boy reaches in and pulls out a chocolate donut, puts that back in the bag then pulls out another chocolate, puts that back in, pulls out another chocolate, puts that one back and then pulls out a coconut. How likely is this series of donuts? E. The boy’s other sister wants coconut, too. This time he reaches in and pulls out four donuts. What is the probability that three are chocolate and one is coconut? F. The boy grabs four donuts, what is the probability that at least one of them is coconut? 3. Nice’s disease, a heritable trait that causes people who suffer from the disease to break chalk while writing on a blackboard 50 times more often than normal people and to write in very small letters near the bottom of the blackboard, is a recessive trait controlled by a single gene. A woman suffering from Nice’s disease marries a normal man. A. If the man is heterozygous at this gene, what is the likelihood that they will have a boy who suffers from the disease? (Assume that male and female children occur with equal frequency.) B. What is the probability that they have a boy or a child with the disease? C. What is the probability that, out of three children, two are girls and two have Nice’s disease? 4. You are bored with genetics problems and decide to flip a coin 10 times. What is the probability of getting two heads and eight tails? 5. In a dihybrid cross with peas, 3/4 of all plants produced had purple flowers, 1/4 had white flowers. Also, 3/4 had yellow seeds and 1/4 had green seeds. A. What proportion of the offspring had purple flowers and yellow seeds? B. Diagram this cross using either a Punnett square or a branch diagram. C. From your diagram, determine what proportion have purple flowers. What proportion have yellow seeds? D. What proportion had both purple flowers and yellow seeds? How does this compare to your answer for A? E. A purple flowered, yellow seeded individual is testcrossed. What are the possible genotypic and phenotypic ratios that could result from this testcross? 6. You conduct a dihybrid cross with Yetis following the alleles at two genes. One gene controls hairiness with baldness being the recessive trait (totally covered with hair is the wildtype). Another gene controls skin color, purple skin is recessive to blue. A. What proportion of the offspring of your cross would you expect to be bald and purple? B. Your cross produced the following results: Hairy w/ blue skin 27 Hairy w/ purple skin 4 Bald w/ blue skin 8 Bald w/ purple skin 1 What would you have expected? C. Are your results significantly different from what you expected? D. What is the probability of getting a deviation from the expected values as great as your results that is due to chance? 7. Graph the critical values of the Chi-square statistic as a function of degrees of freedom. Explain this relationship. 8. The following genotypes and resultant phenotypes for five genes are found in Yetis: + p - blue skin p p purple skin + b - hairy b b bald + h - severe halitosis h h no halitosis f - big feet f f small feet w - dark hair w w abominably white hair A. In the following cross, how many genetically different gametes can be formed by the male parent? + + + + + + + + + p p b b h h f f w w (male) X p p b b h h f f w w (female) B. how many genetically different gametes can be formed by the female parent? C. How many different genotypes are possible in the progeny of this cross? (Hint: think about analyzing each locus individually first.) D. How many different phenotypes are possible in the progeny of this cross? E. What is the probability of obtaining the following genotype from this cross: + + + + + + + + p p b b h h f f w w F. What is the probability of obtaining the following phenotype from this cross: blue skin, bald, big feet, severe halitosis and dark hair 9. Considering meiosis in a human being, what is the probability that all paternally derived chromosomes occur in (or end up in) one gamete? 10. What is the probability of rolling a combination totaling eight on two dice thrown simultaneously? 11. Consider this pedigree: I II III IV ? A. What is the probable mode of inheritance for this trait? B. If individual IV-3 and IV-4 produced a child, what is the probability that it will be affected? 12. Consider this pedigree: I II III IV What is the probable mode of inheritance? Study Guide and Additional Problems 2 Study Questions 1. How is genetic variation created during meiosis? 2. Thomas Hunt Morgan and his students tested the chromosomal theory of inheritance. Describe their experiments and results. Explain how their results demonstrated or supported the chromosome theory. 3. What are the mechanisms of sex determination? Why is an XXY Drosophila female, while an XXY human is male? 4. Explain how a genotype could be expressed in more than one trait. What is this phenomenon called? 5. What hypothesis was being tested when Hershey and Chase performed their experiments with T2 bacteriophages? 6. Explain how the Hershey and Chase experiments are significant. What did they demonstrate with their results? 7. What knowledge was available when Watson and Crick proposed their model of DNA? 8. Explain the different levels or organization of DNA in eukaryotic chromosomes. How are prokaryotic chromosomes different? Why is such complexity necessary? 9. Mendel was unaware of chromosomes. If he had known of them, would he have formulated his laws differently? If yes, how? 10. A phenotypic ratio of 2:1 for a gene locus with two alleles is produced for a trait. This locus also affects another trait with a phenotypic ratio of 3:1. In this last case, the phenotypes are alive: dead. How is this possible? Recommended problems from chapter 13 in Russell: 13.1 – 16, 27 and 37 Recommended problems from chapter 2 in Russell: 2.1, 2, 4, 5, 8 – 11, 13 – 20, 30, 32, 33, 37 and 38 Additional Problems 1. Consider the pedigree below. I II III IV A. What is the probable mode of inheritance? B. Which individuals are likely to be heterozygous? Which are homozygous? Are any hemizygous individuals present? 2. In the blue corn chipper (a hypothetical moth that is a pest on corn) green legs is recessive to the wildtype blue legs and is sex-linked. Some geneticists have recently discovered two autosomal mutations in the blue corn chipper that confer resistance to various insecticides. One dominant mutation associated with the 2 nd chromosome confers resistance to Bt (an insecticide). Another recessive mutant th allele confers resistance to DDT (another insecticide) and is located on the 15 chromosome. A. A blue legged (wildtype) female who is resistant to Bt and DDT mates with a trihybrid male. If a farmer sprays his field with DDT, what proportion of the offspring of this cross are likely to survive? B. What proportion of those survivors will be green legged males? C. What proportion of those survivors will be green legged females? 3. Some eggs from a white-eyed female Drosophila are the product of sex- chromosome non-disjunction and have more than the normal number of sex chromosomes. These eggs are fertilized by sperm from a red-eyed male. A. What are the possible genotypes and phenotypes that could be observed in the offspring? B. The female progeny of this mating are backcrossed to the male parental line. What are the possible outcomes in terms of genotypes and phenotypes? 4. Bolivian Banana slugs may be yellow in color (C C ), orange (C C ) or red R (C C ) and may be covered with mucus and sticky (MM), slightly sticky (Mm) or dry (mm). If a sticky, red slug mates with a dry, yellow slug what will be the appearance of the F ?1What about the F ? 2 5. In Kerguelen cabbages, leaf color can be purple or green. Two true-breeding green cabbages are crossed and the F pla1ts are all purple. In the F , t2e phenotypic ratio was 9/16 purple to 7/16 green. A. Build a model to explain the genetic basis of the observed inheritance pattern. B. Another locus controls striping of the leaves. Striping is a dominant trait. A trihybrid cabbage is testcrossed. What are the phenotypes of the parents and offspring? 6. A locus in Sonoran desert camels is involved with hump formation. When two heterozygous parents mate, 3/4 of the offspring are humped on average and 1/4 are non-humped. Another phenotypic trait is the number of humps on the backs of these camels. On average, when two two-humped parents are mated, 2/3 of their offspring have two humps and 1/3 have one hump. You inherit some camels from a long lost uncle and decide to become a camel breeder. You first mate two two-humped camels and they produce 6 two-humped offspring, 3 one-humped offspring and 3 offspring with no humps. What are the probable genotypes of the parents? (Hint: you may have to try to guess the parents’ genotypes and work out the branch diagaram.)

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