Heterosis, the superiority in one or more characteristics of crossbred organisms relative to their inbred parents, is the basis of the modern cultivars utilized in maize (Zed mays L.). Heterosis is of interest in nondomesticated species due to its relevance to the question "how much polymorphism is maintained in natural populations due to selection?" (Berger, 1976). For maize and certain other domesticated species that employ inbred lines to produce commercial hybrids, knowledge of the mechanisms of gene action producing heterosis could contribute to advances in breeding techniques.