Labrador retrievers are black, brown, or yellow. in a cross of a black female with a brown male, results can be either all black puppies, 1/2 black to 1/2 brown puppies, or 3/4 black to 1/4 yellow puppies. these results indicate which of the following? a) brown is dominant to black. b) black is dominant to brown and to yellow. c) yellow is dominant to black. d) there is incomplete dominance. e) epistasis is involved.

The correct answer is option E, Epistasis is involved

Reason:

In epistasis , expression of genes is masked by the mutant gene. One allele in a gene which is considered as dominant masks the  expression of another allele of the same gene.

In this case the different color puppies are due to the effect of epistasis for instance only black puppies are produced when allele representing black color stops the expression of brown allele on the same gene. like wise some other allele on color gene stops the expression of both black and brown allele and thus yellow color puppies are produce