Additive genes underlie Mendelian inheritance and contribute to heterosis

Mendel proposed the laws of segregation and independent combination in his study. However, he focused on "dominant" characters but left "intermediate" ones. Using genotypic and phenotypic data for four representative genes, we reveal connections between the "intermediate" and "dominant" characters. We demonstrate that the fundamental inheritance patterns of these genes are additive effects on both component and compound traits. Additive effects involving more than two genes generate non-additive effects in hybrids. For compound traits such as grain yield, their inheritance depends on differential patterns of component traits in parents; only parents with optimal balances of reciprocal differences in component traits produce overdominant effects, which is important for hybrid breeding.