But if we have at least one uppercase B, so here or here, then we produce a black coat color. So this is an example of epistasis. Why? Well, because we have an interaction of at least two different pairs of alleles at two different loci that ultimately affect a single trait. And in this particular case, the trait is the color of that dog's coat. So once again, epistasis is when two or more pairs of alleles at different loci interact with one another to basically produce some type of gene or some type of trait.