Dominance Versus Over-Dominance in Heterosis: Evidence from Crosses between Open-Pollinated Varieties of Maize

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Abstract
The results for yield of grain in six open-pollinated varieties of maize and the fifteen possible crosses among the parents obtained from replicated tests at three locations for two years are discussed with reference to heterosis observed in the variety crosses. The crosses excelled mid-parents by approximately 20 percent and the higher parent by 11.5 percent. The observation of the heterosis makes it clear that varieties are not genetically identical with respect to frequencies of genes which affect yield. Admitting genetic divergencies between varieties, any attempt to attribute the extent to which heterosis is accountable in terms of complete dominance or over-dominance is largely speculation when the criterion used requires identical gene frequencies for all populations.