Hypostatic gene

A hypostatic gene is one whose phenotype is masked by the expression of an allele at a separate locus, in an epistasis event.

Example: In labrador retrievers, the chocolate coat colour is a result of homozygosity for a gene that is epistatic to the "black vs. yellow" gene. The alleles determining whether the dog is yellow or black, are that of the hypostatic gene in this event.