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nhutnibo nhutnibo
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10 years ago
A pure-breeding white mouse with a long tail was crossed to pure-breeding pink mouse with a short tail. The F1 progeny were all pink with long tails. These F1 mice were test crossed to white mouse with a short tail.

If the gene controlling colour and the gene controlling tail length in mice are very closely linked, what phenotypes are expected to be the most frequent in the progeny of the test cross?
      

A)Pink, short tail and white, short tail
B)Pink, short tail and white, long tail
C)Pink, long tail and white, long tail
D)Pink, long tail and white, short tail
E)There is not enough information to make a prediction
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10 years ago
Given the results of the F1 cross, it can be determined that Pink and Long are the dominant traits (since purebred white x purebred pink = pink and purebred long x purebred short = long)

This dictates the parental genotypes and F1 cross as:

(white/long) ppLL x PPll (pink/short)
All F1 offspring are PpLl genotype (heterozygous pink and heterozygous long)
Purebred white, purebred short are ppll's, so the next cross is:
PpLl x ppll

When genes are linked, the parental genotypes are the most frequent progeny:
PpLl (Pink with Long Tail) &
ppll (White with Short Tail)

Answer choice D)
Pretty fly for a SciGuy
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