7. In Labrador retrievers, coat color is controlled by genes at two loci that demonstrate epistasis. The first locus has two alleles, one for black pigment and one for brown (chocolate) pigment.
The black allele is dominant. The alleles at the second locus determine if the pigment is
deposited in the fur of the animal. If the dog has two recessive alleles at this locus, no pigment
will be deposited in the fur and the dog will be a yellow lab. If the dog has at least one dominant
allele at this locus and at least one black pigment allele, they will be a black lab. If the dog has
two brown alleles and at least one dominant allele at the second locus, they will be a chocolate
lab.
a. If a dog breeder crosses a yellow lab that is heterozygous for coat color with a black lab that
is heterozygous at both loci, what do you expect the phenotypic ratio of the offspring to be?
Use the box below to write out the Punnett square for this cross: