epistasis /epis″təsis/ [Gk, a standing] , 1. suppression of a secretion or excretion, as of blood, menses, or lochia. 2. an interaction between genes at different loci in which one gene masks or suppresses the expression of the other. Epistasis, which is nonallelic and therefore different from dominance, may be caused by the presence of homozygous recessive alleles at one gene pair, as occurs in the Bombay phenotype, or by the presence of a dominant allele at one locus that counteracts the expression of a dominant allele at the other locus. Compare dominance. −epistatic, adj.
