When two or more genes work together to produce a single trait, it's called epistasis.

Here's a breakdown:

* Epistasis is a genetic phenomenon where the expression of one gene (the epistatic gene) masks or modifies the expression of another gene (the hypostatic gene). Think of it as one gene "stepping on" the other.

* This can lead to complex interactions, where the phenotype (observable characteristic) is not just a simple sum of the individual genes involved.

* An example is the coat color of Labrador Retrievers, where one gene determines whether the pigment is black or brown, and another gene determines whether the pigment is deposited in the fur.

Let me know if you'd like more details or examples!