In Labrador retrievers, the allele for black coat color (B) is dominant to the allele for brown coat color (b). However, if a lab has two copies of the recessive allele for a pigment-depositing gene (e), it can only have yellow coat color. In a cross of two doubly heterozygous black labs (BbEe x BbEe), what fraction of the next generation would one expect to be yellow

4/16 or 1/4

Explanation:

This question involves two genes; one coding for coat color and the other for pigment color. The allele for black coat color (B) is dominant to the allele for brown coat color (b) while two copies of the recessive allele for a pigment-depositing gene (e) can only have yellow coat color.

In a cross between two heterozygotes (BbEe), the following gametes will be produced by each parent: BE, Be, bE and be. Using these gametes in a punnet square (see attached image), the fraction of the next generation (F2) expected to be yellow i.e. have the genotype (__ee) will be 4/16 or 1/4.