Mice can have an agouti coat color or yellow Below are resul

Mice can have an agouti coat color or yellow. Below are results of various crosses of agouti and yellow mice. agouti X agouti all agouti yellow X yellow 2/3 yellow and 1/3 agouti agouti X yellow 1/2 yellow and 1/2 agouti Explain this mode of inheritance based on a single gene locus. Assign genotypes and phenotypes for cross 2, yellow X yellow

Solution

A: This shows normal recessive dominance relation between yellow and agouti allele wherein yellow allele is dominant over agouti allele. Therefore, a cross between homozygous agouti (yy) gives all agouti (yy) progeny and a cross between agouti (yy) and yellow (Yy) gives 1/2 yellow and 1/2 agouti progeny. Since the dominant allele is lethal in homozygous condition, the homozygous dominant genotype is never obtained in the progeny.
B: Yellow x Yellow
Yy x Yy= 2/3Yy (yellow) : 1/3 yy (agouti)
This is due to lethal effect of yellow allele in homozygous condition.