Exam Questions from Exam 1 Basic Genetic Tests Setting up and Analyzing Crosses and Genetic Mapping 1 You are studying three autosomal recessive mutations in the fruit fly Drosophila melanogaster Flies that are homozygous for the hb mutation are humpbacked wildtype flies are straight backed Flies that are homozygous for the bl mutation are blistery winged wild type flies are smooth winged Flies that are homozygous for the st mutation are stubby legged wild type flies are long legged You mate flies from two true breeding strains and the resulting F1 flies are all are straight backed smooth winged and long legged F1 females are then mated to males that are humpbacked blistery winged and stubby legged In the F2 generation among 1000 progeny resulting from this cross you observe the following phenotypes Phenotype Number humpbacked blistery winged and stubby legged humpbacked blistery winged and long legged humpbacked smooth winged and long legged straight backed blistery winged and stubby legged straight backed blistery winged and long legged straight backed smooth winged and stubby legged straight backed smooth winged and long legged 26 flies 455 flies 24 flies 27 flies 4 flies 442 flies 22 flies a The male flies that were bred to the F1 generation in order to produce the F2 generation were humpbacked blistery winged and stubby legged On each of their chromosomes they have the alleles hb bl st Using this notation state the genotype of each of the two true breeding parental strains i e the two strains in the P generation Genotype of one parental strain Genotype of the other parental strain b How many flies are found in the class that is the reciprocal class of the humpbacked blistery winged and stubby legged flies c What is the genetic distance between the hb and bl loci Label your answer with the proper units d What is the genetic distance between the bl and st loci Label your answer with the proper units e Draw a genetic map showing the correct order of the hb bl and st loci 2 The following mouse pedigree shows the segregation of two different mutant traits The mutant trait indicated by the dots is dominant whereas the mutant trait indicated by the stripes is recessive Assume 100 penetrance and no new mutations Squares males circles females Mouse 1 Mouse 2 Mouse 3 Mouse 4 expressing dominant mutant trait caused by the A allele expressing recessive mutant trait caused by the b allele expressing both mutant traits a Assuming that both mutant traits are due to linked autosomal genes that are 6 cM apart fill in the following chart using the allele notation indicated by the key above Blocks in the chart that cannot be filled in conclusively should be indicated as inconclusive NOTE One line of the chart is already filled in correctly for you Number of A alleles Number of a alleles Number of B alleles Number of b alleles 0 2 0 2 Mouse 1 Mouse 2 Mouse 3 Mouse 4 b Assuming that both mutant traits are due to linked autosomal genes that are 6 cM apart fill in the boxes with the alleles possessed by mouse 4 on each of the two homologs of this autosome that are depicted in the diagram below Homolog inherited from mouse 1 Homolog inherited from mouse 2 A or a locus B or b locus c Assuming that both mutant traits are due to linked autosomal genes that are 6 cM apart what is the probability that the mouse indicated by a question mark will show both mutant traits the trait encoded by A and the trait encoded by b d Assuming that the recessive mutant trait is caused by a gene on an autosome and the dominant mutant trait is caused by a gene on the X chromosome fill in the following chart using the allele notation indicated by the key above Blocks in the chart that cannot be filled in conclusively should be indicated as inconclusive X linked Number of A alleles Number of a alleles autosomal Number of B alleles Number of b alleles Mouse 1 Mouse 2 Mouse 3 Mouse 4 e Assuming that the recessive mutant trait is caused by a gene on an autosome and the dominant mutant trait is caused by a gene on the X chromosome what is the probability that the mouse indicated by a question mark will show only the recessive mutant trait assuming that the mouse is born female 3 You are working with a mutant strain of yeast that is dark tan wild type yeast are white The dark tan phenotype of the haploid cells you are working with is caused by two different mutations in the same strain The two mutations are designated drk1 and drk2 a Mating of the drk1 drk2 double mutant to wild type yeast produces diploids that are white Sporulation of these diploids yields 50 tetrads 4 of these tetrads called Type One contain four light tan spores 37 of these tetrads called Type Two contain two dark tan spores and two white spores 9 of these tetrads called Type Three contain one dark tan spore two light tan spores and one white spore Categorize each of the tetrad types as parental ditype PD tetratype TT or nonparental ditype NPD b Are the drk1 and drk2 mutations linked If so give the distance between them Label your answer with the proper units c In yeast 1 cM of genetic distance corresponds to 3 500 base pairs of physical distance An average yeast gene is about 1 400 base pairs long and the longest yeast gene is 14 700 base pairs Keeping this information in mind you select a Type Three tetrad from part a and mate the two light tan spores from that tetrad to each other Can you deduce the color of the resulting diploids If so what color would the diploids be Next you isolate a mutant strain of yeast that cannot grow on medium lacking leucine This strain contains a single mutation you call leu1 The leu1 mutation is near to drk1 on the same chromosome When the leu1 mutant is mated to wild type yeast the resulting diploids cannot grow on medium lacking leucine d You mate leu1 yeast to drk1 yeast and sporulate the resulting diploid You grow the resulting spores on medium containing leucine You then test for growth on medium lacking leucine It is apparent that you have isolated only two types of tetrads 10 tetrads of Type A and 10 tetrads of Type B On medium lacking leucine only two spores from each Type A tetrad can grow both are light tan in color Complete the chart below so as to indicate How many spores from each Type B tetrad can grow on medium lacking leucine and what color is each spore that can grow Type A tetrad Type B tetrad of spores that can grow on medium lacking leucine color of each spore that can grow on medium lacking leucine 2
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