Heterosis in maize: toward prevalence type of intralocus interactions. In the biometrical genetic analysis of maize productivity, performed according to the North Caroline III design, unbiased estimates were used to calculate the average degree of dominance, in which, on average, the effect of linkage was eliminated. The hybrids Rf7×Ku123, MK01×A619 were studied, and unbiased estimates were calculated for four more hybrids according to the literature data. For genes controlling productivity, unbiased estimates of the average degree of dominance ranged from 0.65 to 0.87 for different hybrids. The result indicates that the heterosis effect in maize is more likely to be caused by dominant interactions than over-dominant ones.