Final answer:
The Agouti gene in mice determines the agouti coat color pattern, but the expression of this trait is overridden by the C gene when it is homozygous recessive (cc), leading to albinism. This suppression of the Agouti gene by the C gene is known as epistasis.
Step-by-step explanation:
The Agouti gene, when functioning properly, plays a crucial role in the modulation of coat color in mice by determining the wild-type agouti pattern - a coat with hairs of alternating dark and light bands. This gene's expression is dominant over solid-colored fur. However, another gene, the C gene, controls pigment production. Mice that are homozygous for the recessive c allele (cc) do not produce pigment, resulting in an albino phenotype, and this occurs irrespective of the alleles present at the Agouti locus (A).
Thus, the presence of the cc genotype is an example of epistasis, where one gene suppresses the expression of another gene at a different locus. In a dihybrid cross (AaCc x AaCc), the resulting offspring would have a phenotypic ratio of 9 agouti: 3 black: 4 albino. This demonstrates that the C gene is epistatic to the A gene. Additionally, this genetic mechanism is similar in some aspects to the temperature-sensitive proteins observed in arctic foxes and rabbits, which lead to seasonal color changes, and serves as an adaptation to their environment.