Problem SetsFall 1997(b) You are interested in genes involved in histidine synthesis and have isolatedfour new His- mutants in the a mating type. We will call these mutants 1,2, 3, and 4.You cross each mutant to each of the following test strains: MATo_ His +, MATo_ His2-,and MATo_ His3-. The results of the crosses are given in the table below where a "+"indicates growth of the diploid on medium that lacks histidine and a "-" indicates nogrowth of the diploid on medium that lacks histidine.Mutant 1 Mutant2 Mutant3 Mutant4MATczHis+ + - + +MATo_His2- + - - +MATo_His3- - - - +Give as complete a description as you can of each of the new mutants based on theresults of these tests. Be sure to note any ambiguities that remain.2. Although it is always advisable to use true-breeding lines for geneticexperiments there are some traits for which true-breeding strains cannot beconstructed. A classic example is the yellow coat color allele in mice. Mice that areheterozygous for this allele have yellow fur, but mice that are homozygous are dead.(a) Is the yellow allele dominant or recessive for yellow fur? Is the yellow alleledominant or recessive for lethality?(b) Given a yellow mouse and a wild-type mouse how would you show that theallele for the yellow trait is dominant. Describe the cross(es) that you would do andexplain how the results would be interpreted.(c) In a cross between a yellow mouse and a wild-type mouse what is theprobability of no yellow mice in a litter of six? In a cross between two yellow micewhat is the probability of no yellow mice in a litter of six?(d) A cross between two yellow mice produces a litter of ten with seven yellow miceand three wild-type mice. In test crosses of the yellow F1 mice to wild-type, some wild-type progeny are produced in each test cross. Use the Chi-square test to determinewhether the distribution of genotypes observed among the litter of ten is significantlydifferent (p < 0.05) from the distribution expected if the yellow allele were not lethal inhomozygotes. Please give the observed and expected genotypic ratios, the degreesof freedom, and your calculated value for X2.3. For each of the following pedigrees the individuals expressing a trait areindicated by solid symbols. Consider the following possible modes of inheritance (i)autosomal recessive, (ii) autosomal dominant, and (iii) X-linked recessive. For eachpedigree state which, if any, of the modes of inheritance are not possible unless eitherthe occurrence of a new mutation or incomplete penetrance is invoked. For the modesof inheritance that are possible, calculate the probabilities that the next child indicatedby a (?) will be affected. In the case of X-linked recessive inheritance, calculateseparate probabilities for sons and daughters.(a) (d)?. ?(b) (e)(c) (f)? ?la) Because strains 5 and 5 have dominant alleles that confer canavanine resistance, all crosses involvingthem will result in a canavanine-resistant diploid strain. Since all the other strains have recessivemutant alleles, all crosses with wild-_pe will result in a diploid strain without canavanine resistance.Because strains 1 and 8 are in the same complementation group, crosses between strains I and 8 willresult in a homo_gous mutant diploid; this diploid will therefore be resistant. Similarly, because strains2, 3, and 7 are in a second complementation group, crosses involving any two strains within that groupwill result in a homozygous mutant diploid resistant to canavanine. The same situation is true for crosseswithin strains 4, 9, and I0.lf a particular mutant strain is crossed to different strain which has a mutation in a differentcomplemenmtion group, the resulting diploid will not be resistant to canavanine; complementationhas occurred.(b) You are interested in genes involved in histidine synthesis and have isolatedfour new His- mutants in the a mating type. We will call these mutants 1, 2, 3, and 4.You cross each mutant to each of the following test strains: MATo_ His +, MATc_ His2-,and MATc_ His3-. The results of the crosses are given in the table below where a "+"indicates growth of the diploid on medium that lacks histidine and a "-" indicates nogrowth of the diploid on medium that lacks histidine.Mutant1 Mutant2 Mutant3 Mutant4MATo_His+ + - + +MATc_His2- + - - +MATo_His3- - - - +Give as complete a description as you can of each of the new mutants based on theresults of these tests. Be sure to note any ambiguities that remain.lb) Mutation ] is a recessive mutation, in the same complementation group as the His3 mutation.Mutation 1 isprobably an allele of HIS3.Mutation 2 is dominant to wild-type. No informantion about compIementation can be determined for thismutation.Mutation 3 is a recessive mutation. Itfails to complement both the His2 and His3 mutations. SinceHIS2 and HIS3 are different genes, Mutation 3 could either be a double mutation in both the HIS2 andHIS3 genes, or a large deletion that covers both loci.Mutation 4 is a recessive mutation that complements both the His2- and His3- mutations, i_lutation 4 couldbe a mutation in a novel gene recluiredin the histidine biosynthesis pathway.2. Although it is always advisable to use true-breeding lines for geneticexperiments there are some traits for which true-breeding strains cannot beconstructed. A classic example is the yellow coat color allele in mice. Mice that areheterozygous for this allele have yellow fur, but mice that are homozygous are dead.(a) Is the yellow allele dominant or recessive for yellow fur? Is the yellow alleledominant or recessive for lethality?2a) The yellow allele is dominant for yellow fur, but recessive for lethality.(b) Given a yellow mouse and a wild-type mouse how would you show that theallele for the yellow trait is dominant. Describe the cross(es) that you would do andexplain how the results would be interpreted.2b) Cross the yellow mouse with the wild-type mouse, and look at the coat color of the FI progeny. [fall the F] progeny had wild-b,pe coat color, then the allelefor yellow coat color isrecessive. If half of the £1 progeny had wild-type coat color, with _.heother ha/f having yellowcoat color, then the allele for yellow coat color is domb_ant.t_ In a cross between a.yellow mouse and a wild-type mouse what is the- probability of no yellow mice in a litter of six? In a cross between two yellow micewhat is the probability of no yellow mice in a litter of six?2c) Each newborn mouse in a litter is considered an independent event,
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