The genetic phenomenon where one gene at one locus affects, masks, or modifies the expression of another gene at a different locus is called epistasis.

What epistasis means

Epistasis is an interaction between genes at different loci in which the phenotype produced by one gene depends on the alleles present at another gene.

In classic terms, an allele at one locus can mask or modify the effect of alleles at another locus, so the expected simple Mendelian ratios are altered.

How it works in practice

  • In recessive epistasis , being homozygous recessive at one locus hides the effect of a second gene (for example, certain coat-color pathways where a pigment “switch” gene turns the whole pathway off).
  • In dominant epistasis , a single dominant allele at one locus can override whatever combination exists at the other locus, again changing the phenotypic ratios from the usual 9:3:3:1.

Related terminology

  • When simply saying “one gene at one locus affects another gene at another locus” in an exam or textbook context, the accepted term is epistasis.
  • More generally, this can be described as a gene interaction between loci contributing jointly to a single phenotype, but epistasis is the specific name usually expected.

Meta description (SEO):
Learn what it is called when one gene at one locus affects another gene at another locus: this classic genetics concept is known as epistasis , a key type of gene interaction affecting phenotypes.

Information gathered from public forums or data available on the internet and portrayed here.