Dominance is not necessary for heterosis: a two-locus model

Summary Under a two-locus model with additive genes which combine multiplicatively to determine a quantitative trait, heterosis is generally observed in the F 1 It is positive only if both frequencies of the best allele at each locus are not higher in the same parental population. In the F 2 , heterosis depends on the rate of recombination between the two loci. If linkage is tight, F 1 superiority is nearly halved in the F 2 . But if the two genes are independent, heterosis is maintained in the F 2 at the same level as in the F 1 .