In labrador retrievers, black coats are dominant and brown coats are recessive. what is the genotype of a brown labrador? bb, bb, bb, bb

bb

Explanation:

A single gene coding for coat color in Labrador retriever (dog) is involved here. The allele for black coats (B) are dominant over the allele for brown coat (b) i.e the allele B is capable of masking the expression of allele b in a combined state.

According to Mendel's law of dominance, an organism receives two forms of a gene called alleles for each trait (one from each parent). One allele is capable of masking the expression of its variant form, this allele is called DOMINANT allele while the allele that is masked is called RECESSIVE allele.

Hence, in a heterozygous state i.e. combined form of both alleles, the dominant allele will influence the phenotypic expression. This means that the recessive trait will only be expressed when the the recessive allele is in a homozygous state i.e same

In this case, black coat is the dominant phenotype coded for by allele B while brown coat is the recessive phenotype coded for by allele b. Hence, brown coat (recessive trait) will only be phenotypically expressed when its allele is the same or homozygous (bb).