Type of epistasis where one gene pair cannot function if the other gene pair is homozygous recessive, and vice versa. The underlying explanation is that two enzymes are required for chemical biosynthesis. A cross of A.B . x aabb segretates as A.B / {A.bb +aaB.} in a ratio of 9:7 in the offspring (not to be confused with a 1:1 ratio). This type of epistasis often occurs for the flower color trait of ornamental plants, for example.
BT: epistasis
RT: complementary genes