Problem Sets Fall 1997 b You are interested in genes involved in histidine synthesis and have isolated four 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 indicates growth of the diploid on medium that lacks histidine growth of the diploid on medium that lacks histidine Mutant 1 Mutant2 a and a indicates Mutant 3 Mutant 4 MATcz His MATo His2 MATo His3 Give as complete a description as you can of each of the new mutants results of these tests Be sure to note any ambiguities that remain no based on the 2 Although it is always advisable to use true breeding lines for genetic experiments there are some traits for which true breeding strains cannot be constructed A classic example is the yellow coat color allele in mice Mice that are heterozygous for this allele have yellow fur but mice that are homozygous a Is the yellow allele dominant or recessive dominant or recessive for lethality for yellow fur Is the yellow are dead allele b Given a yellow mouse and a wild type mouse how would you show that the allele for the yellow trait is dominant Describe the cross es that you would do and explain how the results would be interpreted c 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 mice what 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 mice and three wild type mice In test crosses of the yellow F1 mice to wild type some wildtype progeny are produced in each test cross Use the Chi square test to determine whether the distribution of genotypes observed among the litter of ten is significantly different p 0 05 from the distribution expected if the yellow allele were not lethal in homozygotes Please give the observed and expected of freedom and your calculated value for X2 genotypic ratios the degrees 3 For each of the following pedigrees the individuals expressing a trait are indicated by solid symbols Consider the following possible modes of inheritance i autosomal recessive ii autosomal dominant and iii X linked recessive For each pedigree state which if any of the modes of inheritance are not possible unless either the occurrence of a new mutation or incomplete penetrance is invoked For the modes of inheritance that are possible calculate the probabilities that the next child indicated by a will be affected In the case of X linked separate probabilities for sons and daughters a recessive inheritance d b e c f calculate la Because strains 5 and 5 have dominant alleles that confer canavanine resistance all crosses involving them will result in a canavanine resistant diploid strain Since all the other strains have recessive mutant 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 will result in a homo gous mutant diploid this diploid will therefore be resistant Similarly because strains 2 3 and 7 are in a second complementation group crosses involving any two strains within that group will result in a homozygous mutant diploid resistant to canavanine The same situation is true for crosses within strains 4 9 and I0 lf a particular mutant strain is crossed to different strain which has a mutation in a different complemenmtion group the resulting diploid will not be resistant to canavanine complementation has occurred b You are interested in genes involved in histidine synthesis and have isolated four 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 growth of the diploid on medium that lacks histidine Mutant 1 Mutant 2 histidine and a indicates Mutant 3 Mutant4 MATo His MATc His2 MATo His3 no Give as complete a description as you can of each of the new mutants based on the results 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 is probably an allele of HIS3 Mutation 2 is dominant to wild type No informantion about compIementation can be determined for this mutation Mutation 3 is a recessive mutation It fails to complement both the His2 and His3 mutations Since HIS2 and HIS3 are different genes Mutation 3 could either be a double mutation in both the HIS2 and HIS3 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 could be a mutation in a novel gene recluired in the histidine biosynthesis pathway 2 Although it is always advisable to use true breeding lines for genetic experiments there are some traits for which true breeding strains cannot be constructed A classic example is the yellow coat color allele in mice Mice that are heterozygous for this allele have yellow fur but mice that are homozygous are dead a Is the yellow allele dominant or recessive dominant or recessive for lethality for yellow fur Is the yellow allele 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 the allele for the yellow trait is dominant Describe the cross es that you would do and explain 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 f all the F progeny had wild b pe coat color then the allele for yellow coat color is recessive If half of the 1 progeny had wild type coat color with heother ha f having yellow coat 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 mice what is the probability of no yellow mice in a litter of six 2c Each newborn mouse in a litter is considered an independent event b a cross between a yellow mouse and a wild type mouse the probability of a single F progeny being non yellow is i Hence the probability of a litter old having
View Full Document
Unlocking...