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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?

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Solution Preview

Hi there,

Thanks for letting me work on your post. Here is my explanation:

(a) since all F1 offspring are phenotypically wild type, the ...

Solution Summary

The expert determines if naked and hairless mutations alleles are for the same gene.

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Breeding Dihybrid Crosses

In cocker spaniels, black coat color (B) is dominant over red (b), and solid color (S) is dominant over spotted (s). If two dihybrids (Bb Ss) were crossed, which would be produced?

A. black and spotted pure-breeding forms
B. black and solid pure-breeding forms
C. red and solid pure-breeding forms
D. red and spotted pure-breeding forms
E. all of these

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