Question

In Labrador retrievers, coat color is controlled by two interacting genes (B and E). The homozygous recessive ee genotype is epistatic to any combination of alleles at the B gene. In the absence of a dominant E allele, coat color is yellow regardless of the B genotype. If a dominant E allele is present, a B allele results in a black coat, whereas the homozygous bb genotype results in a brown

coat. Which genotype of dog would produce offspring with black coats (all of them) when mated with a yellow lab with genotype bbee?
- BBEE
- bbEE
- BbEe
- bbee

Answer 1

To ensure all offspring have black coats when mated with a yellow lab (bbee), the other dog must have the genotype BBEE, which provides dominant E alleles to mask the yellow color and B alleles for a black coat.

Step-by-step explanation:

In Labrador retrievers, coat color is determined by two genes, B and E, where the presence of the E allele allows the B allele to be expressed, resulting in either black or brown coats. The question concerns the necessary genotype of a dog to ensure all black-coated offspring when mated with a yellow lab with the genotype bbee. Since the yellow lab provides an ee combination, which is epistatic to the B gene, the other parent must provide an E allele to override the yellow coat color.

The only genotype from the options listed that can provide dominant E alleles to all offspring is BBEE, as it ensures the presence of at least one E allele and at least one B allele in all the offspring for a black coat color. The yellow lab's b alleles are irrelevant since a single B allele is sufficient to result in a black coat when combined with an E allele.