Final answer:
You cannot determine the precise genotype of the black Labrador retriever parent just from the fact that they produced three black puppies with a chocolate Labrador, as multiple genotypes could result in this outcome.
Step-by-step explanation:
If you mate a chocolate Labrador retriever with a black Labrador retriever and end up with a litter of three black puppies, you cannot determine the genotype of the black parent for certain without additional genetic information. Labradors' fur color is controlled by two alleles, E and B. B_E_ gives black Labs, bbE_ gives chocolate Labs, and ee_ gives yellow Labs no matter the B allele. Since chocolate is recessive to black (bbE_), the chocolate parent must have the genotype bbE_. However, without knowing the genotype of the black Lab, different crosses could yield all black puppies. If the black Lab is BBEE, BBEe, BbEE, or BbEe, all puppies will be black as they will inherit a B allele from the black parent and a b from the chocolate parent. Therefore, although we know the black Lab must contain at least one dominant B allele, we can't be certain of its exact genotype without further testing or breeding results that show a wider range of inheritance patterns.