In mice, the wild-type coat color agouti results from the presence of the domina
ID: 53227 • Letter: I
Question
In mice, the wild-type coat color agouti results from the presence of the dominant A allele; aa homozygote animals have a black coat. At least one wild-type allele at another gene, C, is needed for the formation of any pigment; cc animals are albino. The A and C genes are unlinked. You cross a true breeding agouti mouse homozygous for A and C wild-type alleles and albino mice, homozygous for mutany a and c alleles. What are the genotypes of the gametes produced by the F1 offspring? You cross two F1 offsping. What are the ecpected phenotypic ratios of the F2 offspring?
a. none
b. 9 agouti : 3 black : 3 brown: 1 albino
c. 1 albino : 1 black
d. 9 agouti : 3 black : 4 albino
Explanation / Answer
The correct answer is d. 9 agouti : 3 black : 4 albino
The parents have the genotypes AACC and aacc. They produce the gametes with genotypes AC and ac. All the F1 offspring have the genotype AaCc.
When two F1 offspring are crosses, they produce the gametes with genotypes AC, Ac, aC, ac. The outcome of genotypes is
AACC - 1, AACc - 2, AaCC - 2, AaCc - 4. All of them are agouti phenotypes, so there are expected 9 agouti
AAcc-1, Aacc - 2, and aacc - 1. There are 4 albino phenotypes.
aaCC - 1, aaCc - 2. There are 3 black phenotypes.
The expected ratio is 9 agouti : 3 black : 4 albino
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