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Dihybrid cross analysis

A locus in mice has been identified as determining pigment production.When parents heterozygous at this locus are mated, 3/4 of the progeny are coloured and 1/4 are albino.Another locus determines the actual coat colour; for example, when two yellow mice are mated,2/3 of the progeny are yellow and 1/3 are agouti.It was noticed that the albino mice cannot express whatever alleles they may have at the independently assorting locus.
a. When yellow mice are crossed with albinos, they produce F1 mice in the approximate proportions of 1/2 albino,1/3 yellow and 1/6 agouti.What are the probable genotypes of the parents?
b. If yellow F1 mice are crossed among themselves, what phenotypic ratio would you expect among the progeny?
c. What proportion of the yellow progeny produced here would be expected to breed true?

Solution Preview

Let's look at the information we are given for each trait separately.

The first trait determines whether a mouse is colored of albino (no color pigment). Mating heterozygous parents produces 3/4 colored offspring and 1/4 albino. This suggests that the trait is caused by one gene with two alleles and the colored allele is dominant to the albino allele.
C = colored
c = albino

Cc x Cc = 1/4 CC, 2/4 Cc, 1/4 cc = 3/4 colored, 1/4 albino

The second trait involves two specific coat colors (yellow and agouti). Mating two yellow mice produces 2/3 yellow and 1/3 agouti. This is not the standard ratio of phenotypes from a Mendelian trait caused by one gene with two ...

Solution Summary

Detailed answered to three questions involving a dihybrid cross with non-standard ratios.