Overdominance

[1] Overdominance has been hypothesized as an underlying cause for heterosis (increased fitness of hybrid offspring).

Possessors of the deleterious allele have lower life expectancy, with homozygotes rarely reaching 50 years of age.

In arctic char population in Finland, fish heterozygous for MHC alleles had fewer cysts, grew larger, and had a better chance at survival, all indicating a higher fitness of the heterozygotes.

Since the emergence of the white allele, the frequency of the red phenotype has been increasing in wild populations in multiple regions of the alps.

This ram was known for its callipyge phenotype (pronounced muscular features and hindquarters) caused by a mutated allele, but only 15% of its offspring received these same traits.