overdominance (superdominance) In genetics, the phenomenon in which the character of the heterozygotes is expressed more markedly in the phenotype than in that of either homozygote. Usually the heterozygote is fitter than the two homozygotes: this can give rise to monohybrid heterosis, the hybrid vigour obtained by crossing parents differing in a single specified pair of allelic genes. See also BALANCED POLYMORPHISM.

overdominance (superdominance) In genetics, the phenomenon in which the character of the heterozygotes is expressed more markedly in the phenotype than in that of either homozygote. Usually the heterozygote is fitter than the two homozygotes: this can give rise to monohybrid heterosis, the hybrid vigour obtained by crossing parents differing in a single specified pair of allelic genes. See also BALANCED POLYMORPHISM.