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MIT 7 03 - Exam I

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Name: ____________________________________17.03 Exam One -- 2005Name: ______________________________Exam starts at 11:05 am and ends at 11:55 am.There are 7 pages including this cover page.Please write your name on each page.Only writing on the FRONT of every page will be graded.(You may use the backs, but only as scratch paper.)Question 1 24 pts________Question 2 30 pts________Question 3 30 pts________Question 4 16 pts________ TOTAL out of 100_______7.03 Fall 205 Exams & Answers1 of 939/5/07Name: ____________________________________21. (24 pts) You are studying two recessive mutations in the fruit fly Drosophilamelanogaster. The hb– mutation causes flies to have hairy backs (wild-type flies havehairless backs). The tl– mutation causes flies to have thick legs (wild-type flies have thinlegs). You mate females from a true-breeding strain with hairy backs and normal legs tomales from a true-breeding strain with normal backs and thick legs. F1 females are thenmated to males that have hairy backs and thick legs to produce F2 progeny. If youanalyzed 500 MALE progeny in the F2 generation, how many flies of each possiblephenotypic class would you expect, given that:(a, 8pts) The two traits are determined by two unlinked autosomal geneshairy thick:hairy thin:hairless thick:hairless thin:(b, 8pts) The two traits are determined by two completely linked genes on the Xchromosomehairy thick:hairy thin:hairless thick:hairless thin:(c, 8pts) The two traits are determined by two autosomal genes that are 20 cM aparthairy thick:hairy thin:hairless thick:hairless thin:7.03 Fall 205 Exams & Answers2 of 939/5/07Name: ____________________________________32. (30 pts) The following pedigree shows the inheritance two different rare traits. Eachtrait is determined by a different gene. The presence of Trait 1 is indicated by dots, and thepresence of Trait 2 is indicated by vertical lines.(a, 6pts) What mode(s) of inheritance is/are consistent with each of the traits segregating inthis pedigree? (Your choices are: autosomal recessive, autosomal dominant, X-linkeddominant, X-linked recessive.) Assume no new mutations and complete penetrance.Trait 1 (dots):Trait 2 (vertical lines):(b, 6pts) State whether the two traits in the pedigree are linked or not linked, or if it isinconclusive given these data.(c, 6pts) What is the probability that the child indicated with a question-mark will show atleast one of the two traits? Show your work.?(Note that no singleindividualdisplays both traits.)7.03 Fall 205 Exams & Answers3 of 939/5/07Name: ____________________________________4Consider this new pedigree, which shows the inheritance of two different rare traits. Eachtrait is determined by a different gene. The presence of Trait 3 is indicated by horizontal lines,and the presence of Trait 4 is indicated by shading.(d, 6pts) What mode(s) of inheritance is/are consistent with each of the traits segregating inthis pedigree? (Your choices are: autosomal recessive, autosomal dominant, X-linkeddominant, X-linked recessive.) Assume no new mutations and complete penetrance.Trait 3 (horizontal lines):Trait 4 (shading):(e, 6pts) State whether the two traits in the pedigree are linked or not linked, or if it isinconclusive given these data.(Note that no singleindividualdisplays both traits.)7.03 Fall 205 Exams & Answers4 of 939/5/07Name: ____________________________________53. (30 pts) You are studying three mutations in yeast. The first mutation causes the Ser–phenotype of being unable to grow without serine in the medium. The second mutation causes theHis– phenotype of being unable to grow without histidine in the medium. The third mutationcauses a small colony phenotype. Wild-type yeast are Ser+ His+ and big. You mate a Ser–haploid mutant yeast to a His– small haploid mutant yeast. You induce sporulation of theresulting diploid, and obtain the following tetrad types. (The number of tetrads of each typethat you get (out of a total of 100) are shown after the tetrad type.)Tetrad Type ASer– His+ bigSer– His+ small 9 tetrads of this typeSer+ His– bigSer+ His– smallTetrad Type BSer– His+ bigSer– His+ big 90 tetrads of this typeSer+ His– smallSer+ His– smallTetrad Type C Ser+ His– bigSer– His+ small 1 tetrad of this typeSer– His– bigSer+ His+ small(a, 4pts) Which Tetrad Types are TTs, NPDs, and PDs with respect to the His and sizegenes?TT:NPD:PD:(b, 4pts) Are the His and size loci linked? If so, what is the genetic distance between them?7.03 Fall 205 Exams & Answers5 of 939/5/07Name: ____________________________________6(c, 4pts) Which Tetrad Types are TTs, NPDs, and PDs with respect to the Ser and sizegenes?TT:NPD:PD:(d, 4pts) Are the Ser and size loci linked? If so, what is the genetic distance between them?(e, 4pts) Which Tetrad Types are TTs, NPDs, and PDs with respect to the Ser and Hisgenes?TT:NPD:PD:(f, 4pts) Are the Ser and His loci linked? If so, what is the genetic distance between them?(g, 6pts) Draw a genetic map showing the correct relative order of the Ser, His, and size loci.If one of the loci is unlinked from the other two, draw it on a separate chromosome.7.03 Fall 205 Exams & Answers6 of 939/5/07Name: ____________________________________74. (16 pts) You are studying a recessive trait in a diploid rodent species in which XX organismsare female and XY organisms are male. This trait is determined by a single gene, but you have noidea where in the genome this gene is located. This rodent has 20,000 distinct genes in itsgenome, 400 of which are found on the X chromosome.(a, 4pts) Given this information, give your best estimate of the probability that the trait you arestudying is X-linked.(b, 12pts) You mate a female rodent displaying the trait to a wild-type male. You then mate anF1 female to a wild-type male to produce F2 offspring, and analyze only the F2 males. The firstthree F2 male offspring display the wild-type phenotype.Given that the first three male F2 offspring show the wild-type phenotype, determine theprobability that the trait you are studying is X-linked. Show all steps of your work, using clearlabels.7.03 Fall 205 Exams & Answers7 of 939/5/07Name: __________KEY____________________17.03 Exam One -- 2005Name: ___________KEY__________Exam starts at 11:05 am and ends at 11:55 am.There are 7 pages including this cover page.Please write your name on each page.Only writing on the FRONT of every page will be


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MIT 7 03 - Exam I

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