Question

A dog breeder liked yellow and brown labrador retrievers. in an attempt to produce yellow and brown puppies, he mated a yellow labrador male and a brown labrador female. unfortunately, all the puppies produced in this cross were black. (see pp. 117–119 for a discussion of the genetic basis of coat color in labrador retrievers.)
a. explain this result.
b. how might the breeder go about producing yellow and brown labradors?

Answer 1

For question a, Labrador retrievers vary in two loci, B and E. Black dogs have dominant alleles at both loci (B-E-), brown dogs have bbE-, and yellow dogs have B-ee or bbee. Since all the puppies were black, a dominant E allele from the brown parent and they must all have inherited a dominant B allele from the yellow parent. The yellow male must have been BBee, and the brown female parent must have been bbEE. The black puppies were all BbEe.

For question b, simply mating yellow with yellow will produce all yellow Labrador puppies. If at least one of the parents is homozygous EE, mating two brown Labradors will produce either all brown puppies, or ¾ brown and ¼ yellow if both parents are heterozygous Ee.