Could you please answer the question and provide a rationale for each answer? Th

Question

Could you please answer the question and provide a rationale for each answer? Thank you!!

1. The genotypes of four strains of Neurospora are unknown. However, we do know that all strains require arginine and have the growth characteristics shown below. Nutrition and Accumulation Growth on Strain Minimal Ornithine Citrulline Arginine Accumulates 1 - - + + Ornithine 2 - - - + Citrulline 3 - - - + Ornithine 4 - - - + Citrulline Pairwise complementation tests of the four strains: 1 1 0 2 2 + 0 3 + = heterokaryon grows on minimal media 3 0 0 0 4 0 = no growth of heterokaryon on minimal media 4 + 0 0 0 Crosses among mutants yielded prototrophs in the following percentages: 1 x 2 25% 1 x 3 none detected among 1 million ascospores 1 x 4 25% 2 x 3 0.002% 2 x 4 0.004% 3 x 4 none detected among 1 million ascospores A. How many distinct mutational sites are represented among these four strains affecting how many polypeptide chains? B. Give the genotypes of the four strains, using a consistent and informative set of symbols. C. Give the map distances between all pairs of linked mutations. D. What percentage of prototrophs would be expected among ascospores of the following types: Strain 1 x wild type Strain 3 x wild type Strain 2 x wild type Strain 4 x wild type

Explanation / Answer

1. The genotypes of four strains of Neurosporaare that all strains require arginine and have the growth characteristics shown below.Nutrition and AccumulationGrowth on Strain Minimal, Ornithine, Citrulline, Arginine. Accumulates1--++Ornithine2---+Citrulline3---+Citrulline4---+Ornithine Pairwise complementation tests of the four strains:11022+03+ = heterokaryon grows on minimal media3+0040 = no growth of heterokaryon on minimal media40000Crosses among mutants yielded prototrophs in the following percentages:1 x 2 25%1 x 4 none detected among 1 million ascospores1 x 3 25%2 x 4 0.001%2 x 3 0.002%3 x 4 none detected among 1 million ascosporesA. How many distinct mutational sites are represented among these four strainsaffecting how many polypeptide chains?B. Give the genotypes of the four strains, using a consistent and informative setof symbols.

The localization of a mutation to a particular chromosome is the first step in genetic mapping of a mutation-definedgene. A simple example involves recessive mutations on the X chromosome in Drosophila. (In fruit flies, as in humans, males are genotypically XY and females are XX.) Such X-linked recessive mutations exhibit a distinctive sex-linkedsegregation pattern in various crosses (Figure 8-16). Mutant males mated to normal, homozygous females produce no phenotypically affected progeny. If the female is homozygous for the mutation, all the sons will have the mutantphenotype and all the daughters will be heterozygous and thus unaffected. If the females are heterozygous, they are phenotypically normal, but they act as carriers, transmitting the mutant allele to 50 percent of their male progeny. Thus any recessive mutation for which these sex-linked segregation patterns are observed can be mapped to the X chromosome.

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