Q. A locus in mice is involved with pigment production; when parents heterozygous at this locus are mated, 3/4 of the progeny are coloured and 1/4 are albino. Another phenotype concerns coat colour; when two yellow mice are mated, 2/3 of the progeny are yellow and 1/3 are agouti. The albino mice cannot express whatever alleles they may have at the independently assorting agouti locus.

a. When yellow mice are crossed with albinos, they produce F1 mice consisting of 1/2 albinos, 1/3 yellow and 1/6 agouti. What are the possible genotypes of the parents?

b. If yellow F1 mice are crossed among themselves, what phenotypic ratio would you expect among the progeny? What proportion of the yellow progeny produced here will be expected to breed true?