A dog with brown fur breeds with a dog with gray fur. When the puppies are born, three of the puppies have brown fur, and one puppy has gray fur. Assuming that there are only two alleles that code for fur color, what is the most likely reason for the puppies' fur colors? A. The allele for brown fur mutated into the allele for gray fur. B. The allele for gray fur is dominant, and the allele for brown fur is recessive. C. The allele for gray fur mixed with the allele for brown fur. D. The allele for gray fur is recessive, and the allele for brown fur is dominant.