Question

The agouti locus in mice has three alleles: a is recessive and confers a black coat, A is dominant to a and confers an agouti coat, and A^Y is dominant to both and confers a yellow coat. A^Y is also a recessive lethal. In addition, the independently assorting c allele is recessive (to C) and prevents the mice from making any fur pigments at all, resulting in albinos. Two mice are crossed, and produce offspring in a ratio of 2 yellow : 1 albino : 1 agouti. What are the genotypes and phenotypes of the parent mice?

  

Answer 1

The genotypes of the parent mice are AAYyCc X AaYyCc.

The phenotypes of the parent mice is Yellow coat.

The coat color alleles 'A' and 'a' in parent mice would be homozygous dominant 'AA' or heterozygous dominant 'Aa'. It can never be homozygous recessive 'aa' because this would have resulted in some black coat offspring which is not here.

The coat color alleles 'C' and 'c' in parent mice would be heterozygous dominant 'Cc' in both. Its is because many offsprings are albino which is seen in homozygous recessive 'cc' i.e., one 'c' allele from one parent and the other 'c' allele from the other parent.

The yellow coat alleles 'Y' and 'y' would always be heterozgous dominant 'Yy' in parent mice because homozygous dominant 'YY' is recessive lethal. Homozygous recessive 'yy' would produce offsprings with other color types other than yellow coat. The yellow coat allele act at recessive allele in its effect on development but act as dominant allele in its effect on coat color.