ABSTRACT
The phenomenon of heterosis is defined by Shull (1911) as “the superiority of heterozygous genotypes with respect to one or more characters in comparison with the corresponding homozygotes. Heterosis is the phenotypic result of gene interaction in heterozygotes and thus confined (at least in maximal amount) to that state.” Hence, to observe heterosis, the F1 must be superior to the two breeding lines that are its parents. Nevertheless, the heterozygote may also be inferior to both homozygotes. This performance is defined as negative heterosis (Jinks 1983).
