Final answer:
An epistatic gene masks or interferes with the expression of another gene, termed a hypostatic gene. Epistasis involves genes that are part of a metabolic pathway where one gene's expression depends on another's function.
Step-by-step explanation:
A gene that affects, prevents, or masks the expression of a gene at another locus is known as a epistatic gene. Epistasis occurs when the interaction between genes is antagonistic, such that one gene masks or interferes with the expression of another. This means that the epistatic gene is dominant over the other gene, which is termed the hypostatic gene, and it may alter or completely suppress the hypostatic gene's manifestation.
The biochemical basis of epistasis often lies in a gene pathway where the expression of one gene is dependent on the function of another gene that either precedes or follows it within the pathway. For instance, if a gene is responsible for the production of an enzyme that is critical in a metabolic pathway, and another gene interferes with the production or function of that enzyme, the second gene would be considered epistatic with respect to the first.