2.5.2 Example of epistatis (Minkema 1966)

Plumage pattern in chicken is amongst other genes, determined by interacting alleles of two different loci: the E-locus and the S-locus. The E-locus has two alleles E and e^+. The S-locus: S and s. E is dominant over e⁺ and causes a uniform black plumage. In the e⁺e⁺ animals the black colour is restricted to restricted parts of the plumage. In the non-black parts of the plumage the SS or Ss animals have at these places the silver colour, while the ss animals have there the golden colour. Thus the golden or silver colour is only expressed in the e⁺e⁺ animals: black at the E-locus  is dominant over golden and silver determined by the alleles at the S-locus.