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MIT 7 03 - Study Guide

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Problem_Set_1_Problem_Set_2Problem_Set_3Problem_Set_4Problem_Set_5Problem_Set_67.03 FALL 2009 PROBLEM SET 1 Due: September 23, 2008 1. (15 points) You have isolated a collection of yeast mutants that form dark tan colonies (wild type yeast are white). Dark mutants 1–5 are MATa and mutants 6–10 are MATα. Your analysis begins by pairwise mating of each mutant to a wild-type strain and to the mutants of the opposite mating type. The color of the colonies of the resulting diploids are shown in the table below. a \ α Wildtype Mutant 6 Mutant 7 Mutant 8 Mutant 9 Mutant 10 Wildtype White White White Dark White White Mutant 1 White Dark White Dark White Dark Mutant 2 White White White Dark White White Mutant 3 White White White Dark White White Mutant 4 White Dark White Dark White Dark Mutant 5 White White Dark Dark Dark White a) Which of the mutants are dominant and which are recessive (2ps)? b) Organize the mutants into complementation groups (genes), indicating any ambiguities. (9 pts) c) Based on these complementation data, what is the minimum number of genes represented by this collection of dark mutants? What is the maximum number of genes? (4 pts) 2. (18 points) In a large-scale breeding population, two female flies with vestigial wings (short-winged flies) arise from different parents. You would like to know whether the two mutations that caused this vestigial wing phenotype are in the same gene or in different genes. Assume that you have an unlimited number of true-breeding flies with normal wings. Describe a set of crosses you would perform to make this determination and their outcomes. In your description, please indicate a set of circumstances that would prevent you from easily making this determination. 13. (32 points) Say fur color in mice is determined by 2 genes. One gene determines what color pigment is produced, and another gene determines whether or not any pigment is produced at all. Suppose black fur is dominant to brown fur, but a mutation in the other gene prevents pigment of either color from being produced so the mice are white. You cross a true-breeding brown mouse with a true-breeding white mouse. a) Determine the ratio of each color mouse in the F2 generation if the F1 progeny are black. (4 pts) b) Determine the ratio in the F2 generation if the F1 progeny are white (Assume the parental white mice had only one mutation). (4 pts) c) When you performed this cross, all the F1 progeny were black. These all have the same genotype, but the black mice in the F2 generation have more than one genotype. You wish to determine the genotype of one of the black F2 mice, so you back cross to a heterozygous F1 mouse. For each possible genotype determine the expected ratio of fur colors in the progeny. (10 pts) d) You get 40 progeny from your test cross, of which 32 are black and 8 are brown. You think you know the genotype but your lab partner thinks it could still be two genotypes. Use the chi square test to determine if you can reject one of the remaining hypotheses. The table below gives chi square values for 1, 2 and 3 degrees of freedom. Use the convention that for p < 0.05 there is a statistically significant difference between the observed results and the results expected for a given model and therefore we can reject the model on the basis of the experimental data. (14 pts) p value: .995 .975 0.9 0.5 0.1 0.05 0.025 0.01 0.005 df = 1 .000 .000 .016 .46 2.7 3.8 5.0 6.6 7.9 df = 2 .01 .05 .21 1.4 4.6 6.0 7.4 9.2 10.6 df = 3 .07 .22 .58 2.4 6.3 7.8 9.3 11.3 12.8 24. (31 points) Consider a cross of two mice whose genotypes for five independently segregating traits are Strain 1: DdEEFFGgHH and Strain 2 DdEeffGgHH. Capital letters indicate the dominant alleles, and the all of the traits are independently scoreable. (a) How many different types of gametes can each parent produce? (4 pts) (b) How many different phenotypes can result from this cross? How many different genotypes? (9 pts) (c) What fraction of the progeny will be phenotypically identical to the first parent? To the second parent? (4 pts) (d) i. What fraction of the progeny will be genotypically identical to the first parent? What fraction will be identical at four of the five loci? (4 pts) ii. What fraction of the progeny will be genotypically identical to the second parent? At four loci? (4 pts) (e) One of the progeny of the above cross has the phenotype "d" "E" "F" "g" "H". What cross should you perform to determine the genotype? (6 pts) 35. (32 points) The following is a pedigree from a family with a rare, autosomal recessive disorder. In this question, R represents a dominant allele and r represents a recessive allele. Please note that this imaginary pedigree is from a society in which brother-sister marriages are common. B A 4 (a) What is the probability that individual A has genotype Rr? (2 pts) (b) What is the probability that individual E has genotype Rr? (2 pts) (c) i. What is the probability that G, when born, will be affected? (6 pts) ii. What is the probability that G will have genotype Rr (9pts)? Suppose that individual G is born, and does not have the disease. (d) What is the probability that individual G has genotype Rr? (4 pts) (e) What is the probability that individual E has genotype Rr, given that G has genotype Rr? (9 pts) D C E F Not affected Affected G?1 7.03 FALL 2009 PROBLEM SET 2 Due: October 2, 2009 1. (24 points) You are studying three autosomal mutations in the fruit fly Drosophila melanogaster. The cw– mutation gives the recessive “curly-wing” phenotype (wild-type flies (cw+) are straight-winged), the sh– mutation gives the recessive “short-bristled” phenotype (wild-type flies (sh+) are long-bristled), and the nh–mutation gives the recessive “no-bristled” phenotype (wild-type flies (nh+) are long-bristled). a) You mate a homozygous nh– cw+ sh– fly (which is no-bristled and straight-winged) to a true-breeding long-bristled and curly-winged fly to obtain an F1 generation. List all phenotypic categories of the flies in the F1 generation and the ratio in which these phenotypic categories are found in the F1 generation. The possible phenotypic classes are: short-bristled and curly-winged, long-bristled and straight-winged, short-bristled and straight-winged,


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MIT 7 03 - Study Guide

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