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MIT 7 03 - Exam 1

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7.03 Exam 1 Name: Section: TA: Exam starts at 11:05 and ends at 11:55 There are five pages including this cover page Please write your name on each page. Please... • Look over the entire exam so you don’t spend too much time on hardquestions leaving easy questions unanswered. • Check your answers to make sure that they make sense. • To help us give partial credit, show your work and state any assumptions that you make. Question 1 30 points Question 2 25 points Question 3 20 points Question 4 25 pointsName: 1. You are studying the genetics of a new insect species and have identified three different recessive traits. For simplicity we will designate the phenotypes of the three distinct recessive traits a, b, and c and the corresponding wild-type phenotypes with a “+”. Two different true-breeding lines are crossed and the F1 progeny all appear as wild-type. These F1 progeny are then crossed to individuals from a true breeding line that has all three recessive traits (a b c) and 100 progeny from this cross are analyzed. The phenotypes and numbers are as follows: Phenotype Number + + + 3 a b c 7 a + c 34 + b + 36 + b c 8 a + + 12 (a 5 pts.) What are the genotypes of the two parental true-breeding lines? (b 5 pts.) Why are there only six phenotypic classes, rather than eight? (c 10 pts.) Give as much information as you can about the chromosomal positions of the three markers a, b, and c. Include in your answer any relevant map distances in cM. (d 10 pts.) Given the map distances in part (c), if F1 insects are crossed to one another, what frequency of the resulting F2 progeny would have all three recessive traits (i.e. phenotype: a b c)?Name: 2. The following mouse pedigree shows the segregation of both a dominant and a recessive trait. (Assume all phenotypes are completely penetrant and that no new mutations arise). (a 5 pts.)What is the genotype of mouse 1? For your answer use D to designate the allele for the dominant trait (with d representing the corresponding wild type allele) and r to designate the allele for the recessive trait (with R representing the corresponding wild type allele) (b 5 pts.) If the genes for both traits are 30 cM apart on the X chromosome, what is the probability that a female progeny mouse indicated by ? will show both traits? (c 7 pts.) If the genes for both traits are 30 cM apart on the X chromosome, what is the probability that a male progeny mouse indicated by ? will show both traits? (d 8 pts.) If the genes for both traits are 30 cM apart on the same autosome, what is the probability that a progeny mouse indicated by ? will show both traits?Name: 3. You have isolated two different mutants of phage l that make fuzzy plaques, which you name fz-1– and fz-2– . You cross fz-1– phage with fz-2–phage by coinfecting E. coliwith phage of both types. Of 1000 plaques that result from the cross, all but 15 are fuzzy. (a 8 pts.) What is the distance between the fz-1– and the fz-2– mutations in map units? Mutations in the cI gene give clear plaques whereas wild-type phage have turbid plaques. (b 12 pts.) You cross of a cI– fz-1– double mutant to a fz-2– mutant and examine a total of 1000 plaques. Among the 15 plaques that are not fuzzy produced in this cross, 12 are clear and 3 are turbid. Draw a genetic map showing the order of the cI– , fz-1–, and fz-2– mutations as well as any relevant map distances in map units.Name: 4. (a 5 pts.) You have isolated a new His– yeast mutant. When you mate this mutant to a wild type yeast strain (His+) you find that the resulting diploids are His+. What does this tell you about the mutant that you isolated? (b 10 pts.) When you sporulate the His+ diploid from part (a) you find that tetrads of three types are produced. From a total of 100 tetrads, the following tetrad types are seen: Type: 2 His– : 2 His+ 3 His– : 1 His+ 4 His– Number: 65 30 5 What does this result tell you about the original His– strain? Give any relevant genetic distances (in cM) that you can calculate. (c 10 pts.) There are a total of 240 His– spore clones in the tetrads from part (b). If you picked two of these His– clones (of opposite mating type) at random and mated them, what is the probability that the resulting diploid would be His+? (You may find it helpful to consider the genotypes of the His– spores in each tetrad type).7.03 Exam 2 Name: Section: TA: Exam starts at 11:05 and ends at 11:55 Please write your name on each page. Only writing on the front sides of each page will be graded Question 1 40 points Question 2 26 points Question 3 34 pointsName: 1. (a 6 pts.) The Mot genes of E. coliare required for motility. You have isolated a nonmotile mutant that you designate Mot1– . You grow P1 phage on an otherwise wild type strain that carries a Tn5 insertion that is linked to one of the Mot genes and then use the resulting phage lysate to infect a Mot1– strain. From 50 transductants isolated by selecting for Kanr you find that 35 are motile and 15 are nonmotile. What is the distance between the Tn5 insertion and the Mot1– mutation (expressed as a cotransduction frequency)? (b 6 pts.) You grow P1 phage on one of the nonmotile, Kanr transductants (Tn5 Mot1–) isolated above and use the resulting phage lysate to infect a second nonmotile strain that carries a mutation designated Mot2– . A total of 200 Kanr transductants are isolated and none are motile. Does this result tell you whether the Mot1– and Mot2– mutations are linked? Explain why or why not. (c 8 pts.) Next, you grow P1 phage on a strain that carries both the Tn5 insertion and the Mot2– mutation. When the resulting phage lysate is used to infect a strain that carries the Mot1– mutation, you find that 5 out of 200 Kanr transductants are motile. Based on this result as well as the results from parts (a) and (b), draw a map showing the relative order of the Tn5 insertion and the Mot1– and Mot2– mutations.Name: (d 6 pts.) You can detect the protein products of the Mot genes. You observe that one of these proteins is 58 kDa in a wild type strain but is 40 kDa in a Mot1– mutant and 30 kDa in a Mot2– mutant. Given this information, draw a diagram showing the direction of transcription of the Mot gene relative to the position of the Tn5 insertion. (e 6 pts.) You introduce an amber suppressing allele of a tRNAser gene into a Mot1– mutant strain. The Mot protein


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