Epistasis ("epi + stasis = to sit on top '') is an interaction between alleles at two different gene loci that affect a single trait, which may sometimes resemble a dominance interaction between two different alleles at the same locus. Epistasis modifies the characteristic 9: 3: 3: 1 ratio expected for two non-epistatic genes. For two loci, 14 classes of epistatic interactions are recognized. As an example of recessive epistasis, one gene locus may determine whether a flower pigment is yellow (AA or Aa) or green (aa), while another locus determines whether the pigment is produced (BB or Bb) or not (bb). In a bb plant, the flowers will be white, irrespective of the genotype of the other locus as AA, Aa, or aa. The bb combination is not dominant to the A allele: rather, the B gene shows recessive epistasis to the A gene, because the B locus when homozygous for the recessive allele (bb) suppresses phenotypic expression of the A locus. In a cross between two AaBb plants, this produces a characteristic 9: 3: 4 ratio, in this case of yellow: green: white flowers.
what type of genetics relationship produces traits utilizing 3 or more genes
Epistasis Epistasis epistasis epistasis