Vanessa 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, Vanessa crosses naked and hairless mice with each other. All the offspring are phenotypically wild-type. After intercrossing these F1 mice, however, Vanessa observes 115 wild-type mice and 85
mutant mice in the F2.
(a) Are the naked and hairless mutations alleles for the same gene?
(b) Using these symbols:
n = naked mutation, N = wild-type allele, h = hairless mutation, H = wild-type allele Indicate the genotypes of the parents, the F1, and each of the phenotypic classes of the F2 progeny. Describe any gene interactions in this set of crosses.
i. parental genotypes: _ ___________________
ii. F1 genotypes: ________________________
iii. F2 Genotypes Phenotypes
F2 genotype ratio: _______________________
F2 phenotype ratio: ____________________
66-X143 Final Examination
(c) What is the most likely explanation for the segregation of wild type and mutant mice in the F2?