Final answer:
The interaction of E and B alleles determining the fur color of Labrador retrievers, where one gene modifies the expression of the other gene, is an example of epistasis.
Step-by-step explanation:
Labrador retrievers' fur color is controlled by two alleles, E and B. Any dog with the ee__ genotype develops into a yellow lab, while B_E_ dogs become black labs and bbE_ dogs become chocolate labs. This variation in color based on the interaction between these two genes is an example of epistasis.
Epistasis occurs when the expression of one gene is dependent on the genotype of another gene. An example of epistasis is also seen in mice, where pigment production is necessary for the coat color to express. In this case, the 'C' gene is epistatic to the 'A' gene. If a mouse is homozygous recessive for the C gene (cc), it will be albino, irrespective of its A gene allele. Thus, genotypes like AACc, Aacc, and aacc all result in the same albino phenotype, further illustrating the concept of epistasis.