Heterosis for characters governed by two genes

Abstract

An expression for heterosis over midparent is derived for characters governed by one gene when hybrids are made using arbitrarily inbred parents. It is shown that, so long as inbreeding does not depress the vigour and fitness of parents, heterosis in hybrids between them will be greater than that obtained in hybrids between open-pollinated parents. The expression derived tor heterosis for characters governed by two genes has brought to focus the possibilities of obtaining heterosis without the presence of dominance etfects, and also of dominance interactions. Arguments are advanced to illustrate that pure dominance hypothesis alone cannot account tor the observed heterosis when the character is under the control of more than one gene. It is found feasible that pure additive gene action at individual genic level coupled with a favourable additive x additive interaction can produce heterosis when gene frequency differences can be ensured. Implications of thisresult to problems in plant breeding are discussed.