Question

Paragraph Styl VI. Vivien has obtained two true-breeding strains of mice, each homozygous for an independently discovered recessive mutation that prevents the formation of hair on the body The discoverer of one of the mutant strains calls his mutation naked, and the other researcher calls her strain hairless. To determine whether the two mutations are simply alleles for the same gene, Viviane crosses naked and hairless mice with each other. All the offspring are phenotypically wild-type. After intercrossing these F1 mice, however, Vivien observes 115 wild-type mice and 85 mutant mice in the F2. a. What is the most likely explanation for the segregation of wild-type and mutant mice in the F2? Explain your answer. (2 points) 9:7 b. Using symbols of your own choosing, indicate the genotypes of the parents, the F1. and each of the phenotypic elasses of the F2 progeny. (2 points)

Answer 1

If two mutants with similar phenotypes are crossed and the resultant F1 exhibits the mutant phenotype, it means that both the mutants are allelic to each other i.e. they are located at the same locus.
If two mutants with similar phenotypes are crossed and the resultant F1 exhibits the WT phenotype, it means that both the mutants are not allelic to each other i.e. they are located at different loci.

In the given case, both the mutations are non-allelic to each other.
F2 phenotypic ratio = 115:85 = Approximately 9:7 ratio

This is an example of epistasis (Complementary gene action)
If both genes are exhibiting Mendelian independent assortment, a phenotypic ratio of 9:3:3:1 is expected.

WT allele for gene 1 = A
Mutant allele for gene 1 = a
WT allele for gene 2 = B
Mutant allele for gene 2 = b

Parental cross: aaBB X AAbb
F1 progeny: AaBb
F1 selfing: AaBb X AaBb
F2 progeny:
A_B_ = 9 = Hairy (WT) mice
aaB_ = 3 = Hairless (mutant) mice
A_bb = 3 = Hairless (mutant) mice
aabb = 1 = Hairless (mutant) mice