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Gen 371 Midterm Exam 2010 (white)

Gen 371 Midterm Exam 2010 (white) - Gen 371 Midterm Exam...

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1/26/11 4:20 PM Gen 371 Midterm Exam 2010 (white) Page 1 of 8 http://courses.washington.edu/au371mkr/resources/problems/midterm_white.html Midterm exam key (white version) 5 Nov 1. Sonia has isolated two haploid mutant yeast strains that are able to survive and grow on plates containing high concentrations of salt (which would kill wild type yeast). (a) A simple mating experiment revealed that both mutations are dominant over wild type. In the outline of the culture plate, illustrate the result that must have led to this conclusion for one of the mutants. Give all the relevant genotypes. Use shading to indicate growth; use n and N for wild type and mutant alleles, respectively. (b) Because the mutations are dominant, she cannot do a complementation test to see if they are alleles of the same gene. Instead, she crosses the two haploid mutants to each other, lets the diploid undergo meiosis, and examines the haploid spores from many tetrads, to determine if the mutant alleles represent two independently assorting genes. In the table, predict the outcomes of the two scenarios (alleles of one gene vs. mutations in two independently assorting genes)--what fraction of spores will grow vs. not grow on high salt, and the underlying genotype(s): Scenario Diploid genotype Spore phenotypes Alleles of one gene (mutant alleles = N 1 and N 2 , wild type = n) N 1 / N 2 Fraction of spores that can grow on high salt: All Their genotype(s): N 1 and N 2 in equal proportions Fraction that cannot grow on high salt: (none) Their genotype(s): Two independently assorting genes (mutant alleles = N and A, wild type = n and a, respectively) Nn Aa Fraction of spores that can grow on high salt: 3/4 Their genotype(s): NA, Na, n A Fraction that cannot grow on high salt: 1/4 Their genotype(s): na (c) Suppose Sonia wanted to select a plasmid containing gene N (either wild type or mutant, your choice) from a genomic DNA library made by inserting XbaI-digested yeast genomic DNA into the vector shown. What genotype yeast should she ideally Home Course mechanics Help hours Calendar Syllabus Lectures, Podcasts Quiz Sections Practice problems Exams GoPost Send email to class Useful links The Gradiator
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1/26/11 4:20 PM Gen 371 Midterm Exam 2010 (white) Page 2 of 8 http://courses.washington.edu/au371mkr/resources/problems/midterm_white.html use to make the DNA library? N (mutant) Which item(s) on the vector will be useful during construction of the library and transformation of E. coli? E. coli origin of replication, Amp r , XbaI site, lacZ Having amplified the library in E. coli, what genotype yeast should she transform? n (wild type) How would she select for a yeast clone with the plasmid of interest? (Be brief!) Plate directly on high salt plate, look for colonies that are able to form. Note: The main points here are that the DNA library should contain the dominant allele of the gene of interest, and that the recipient yeast cells should have the recessive allele -- otherwise there would be no change in phenotype of the cells upon introduction of plasmid. And,
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