THE ROLE OF EPISTASIS AND BACKGROUND GENOTYPE IN THE EXPRESSION OF HETEROSIS

The genetical control of heterosis is usually explained in terms of ad ditive/dominance gene action and digenic interaction of segregating lo ci, and the contribution of epistasis categorized either as duplicate or complementary following the classical relationships observed among the Mendelian genes. In this paper we have explored the alternative re lationships between the additive/ dominance/epistatic components for o btaining classical ratios and investigated their role in promoting het erosis. The study has shown that while the classical duplicate and com plementary relationships supress heterosis, other relationships not on ly boost its magnitude but also allow more or less unrestricted expres sion of genotypic variation in the F, generation. Removal of another i mportant restriction of no interaction between the segregating loci an d the background genotype further revealed that heterosis is boosted i n the presence of such interactions. However, these interactions do no t affect the genetical interpretation of heterosis because their contr ibution is maximized only when the parental lines display dispersion o f alleles at the segregating loci and dominance is unidirectional.