Vanessa has obtained two true-breeding strains of mice, each homozygous for an i

Question

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. (Cross 1 ) All the offspring are phenotypically wild-type.

A) What is the most likely explantion for the phenotypes fo the F1 mice? Are they naked and hairless mutations alleles for the same gene?

B) Vanessa next intercrosses in the F1 mice (Cross 2) and based in the F2 phenotype ratios, concludes that there is no gene interation. Fill out the following information for the F1 intercross and F2 progeny. Use these symbols: n= naked mutation , N= wild-type allele, h= hairless mutation, H= wild type allele.

Cross 1: parental genotypes:________________________

F1 genotypes:____________________________

Cross 2: Write out a punnett square for the F1 intercross and give the F2 phenotype ratio:

F2 phenotype ratio __________________

Explanation / Answer

n=nake allele; N= normal allele
h=hairless allele; H= normal allele

P: 'nake' (nnHH) x 'hairless' (NNhh)
F1: all NnHh (wild type/normal type)

Generally, a phenotype is 'said' based on the mutant, so P1 is just said as 'nake' (not as 'nake-normal'), and P2 is as 'hairless' (not as 'normal-hairless') so both allels are not for the same gene

B)

NH

Nh

nH

nh

NH

NNHH wild

NNHh wild

NnHH wild

NnHh     wild

Nh

NNHh wild

NNhh wild hairless

NnHh wild

Nnhh wild hairless

nH

NnHH wild

NnHh wild

nnHH naked wild

nnHh naked wild

nh

NnHn wild

Nnhh wild hairless

nnHh naked wild

nnhh naked hairless

wild- wild : wild- hairless: naked wild : naked hairless

9: 3:3:1

NH

Nh

nH

nh

NH

NNHH wild

NNHh wild

NnHH wild

NnHh     wild

Nh

NNHh wild

NNhh wild hairless

NnHh wild

Nnhh wild hairless

nH

NnHH wild

NnHh wild

nnHH naked wild

nnHh naked wild

nh

NnHn wild

Nnhh wild hairless

nnHh naked wild

nnhh naked hairless

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