TABLE 1

The relationships among the eight genetic parameters producing digenic segregation ratios in the F₂ generation characteristic of classical epistasis (from Jana 1971)

Nature of epistasis	Relationship among parameters^{^a}	F₂ ratio
Complementary	A₁ = A₂ = D₁ = D₂ = AA₁₂ = AD₁₂ = AD₂₁ = DD₁₂	9:7
Duplicate	A₁ = A₂ = D₁ = D₂ = −AA₁₂ = −AD₁₂ = −AD₂₁ = −DD₁₂	15:1
Dominant	A₁ = D₁ ≠ A₂, A₂ = D₂ = −AA₁₂ = −AD₁₂ = −AD₂₁ = −DD₁₂	12:3:1
Recessive	A₁ = D₁ ≠ A₂, A₂ = D₂ = AA₁₂ = AD₁₂ = AD₂₁ = DD₁₂	9:3:4
Inhibitory	A₁ = −A₂ = D₁ = −D₂ = −AA₁₂ = −AD₁₂ = −AD₂₁ = −DD₁₂	13:3

↵^a Ai is the additive effect at locus 1; A₂ is the additive effect at locus 2; D₁ is the dominance effect at locus 1; D₂ is the dominance effect at locus 2; AA₁₂ is the interaction between A₁ and A₂; AD₁₂ is the interaction between A₁ and D₂; AD₂₁ is the interaction between A₂ and D₁; and DD₁₂ is the interaction between D₁ and D₂.