7.03 Exam 1 ReviewTAs: Brian Chin ([email protected]) Ashlie Brown ([email protected])Exam 1 Tutorial: Tues, 10/4 7-9:30pm 66-1687.03 Archive: http://web.mit.edu/7.03/resources.shtml1.) You have isolated three mutants, his1, his2 and his3 that are unable to growwithout the amino acid histidine. You mate each of these with a wild type strainof the opposite mating type and analyze the resulting diploid for its ability to growwithout histidine. You get the following results:MatingDiploid’s phenotypehis1 x wildtypeWThis2 x wildtypeWThis3 x wildtypeHis-a) What does this tell you about each of the mutations?b) You mate his1 with a his2 strain of the opposite mating type. The resultingdiploid is unable to grow on histidine. What does that tell you about these twomutations?c) You decide to mate your his1 and his3 mutants and then sporolate theresulting diploids. You analyze the resulting tetrads for their ability to growwithout histidine: X= No Growth = Growth123456789101112131415161718XXXXXXOXXXXOXOXXXXXXXOXXXXXOXXXXXXXXXXXXXXXXXXXXXOXOXXXXXXXXXXXXXXOXXXXXd) How many PD, TT and NPD are there?e) Are these two genes linked? If so then by how far?2.) Wild-type Drosophila have red eyes, and white eyes is an X-linked recessivephenotype caused by a single mutation. A new single mutation that gives therecessive phenotype of apricot colored eyes is isolated. A female from a true-breeding apricot-eyed strain is crossed to a male from a true-breeding white-eyed strain. All of the resulting F1 flies have apricot eyes.(a) Are the white-eye and apricot-eye mutations in the same gene or in differentgenes? Explain your answer.A collection of apricot-eyed F1 females from the cross described above aremated to males from a true-breeding white-eyed strain, and 1000 male progenyare examined. Among these progeny, only 6 flies have normal red eyes.(b) What is the measured distance between the white-eye and apricot-eye loci incM?A new mutation is isolated that causes the recessive eye color “peach.” A femalefrom a true-breeding peach-eyed strain is crossed to a male from a true-breedingwhite-eyed strain. All of the resulting F1 females have normal red eyes and all ofthe resulting F1 males have peach eyes.(c) Is the peach-eye mutation on an autosome or on the X-chromosome? Explainyour answer.(d) Are the white-eye and peach-eye mutations in the same gene or in differentgenes? Explain your answer.A mutation that causes the recessive phenotype of crossveinless wings lies onthe X-chromosome. A female from a true-breeding strain with apricot eyes andcrossveinless wings is crossed to a male from a single mutant true-breedingstrain with white eyes and normal wings. As expected, all of the F1 females fromthis cross have apricot eyes and normal wings. A large collection of these F1females are crossed to wild-type males and 10,000 male progeny are examined.The observed phenotypes are as follows:(e) Draw a genetic map showing the relative order of the crossveinless, apricotand white loci.3.) You are studying a completely penetrant human disorder that is rare in thegeneral population but relatively common in certain regions. Woman #1, whosemother’s brother was afflicted with this disorder, is trying to determine theprobability that she and her husband would have an affected child. Woman #1’shusband’s sister ultimately died of the disease. Woman #1’s father is from alow-risk population, but everyone else in the pedigree is from a region where thedisorder is common. Besides the two individuals mentioned, no one else in thispedigree, including the parents of the affected individuals, is/was affected withthe disease. All cases of this disorder are suspected to be caused by mutationsin the same gene.(a) Draw the pedigree of this family, indicating the genotypes of individualswhere possible.Normal wingsWhite eyes4,418Crossveinless wingsApricot eyes4,330Normal wingsApricot eyes610Crossveinless wingsWhite eyes590Normal wingsRed eyes2Crossveinless wingsRed eyes50(b) Is this disorder recessive or dominant? Is it X-linked or autosomal?(c) If the couple’s first child is affected, what is the probability that the couple’ssecond child will be affected?(d) What is the probability that the couple’s first child will be affected?(e) If the couple’s first child is not affected, what is the probability that Woman #1is a carrier of the
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