The maintenance of transferrin polymorphism in pigeons

Abstract

Transferrin, a nonheme iron-binding protein, is polymorphic in most vertebrate species that have been examined. In pigeons, it is controlled by an autosomal gene, with two known codominant alleles, TfA and TfB. The two alleles are found in nearly equal frequencies and the three genotypes are at Hardy-Weinberg equilibrium in all populations studied. This report shows that ovotransferrins from heterozygous females inhibit microbial growth, by use of yeast as an assay organism, better than ovotransferrins from either of the homozygous types, or those from a mixture of homozygous types. Heterozygous females hatch a larger percentage of their eggs than homozygous females. This difference is probably accounted for by the transferrin effect. The failure of the mixture of the homozygous types to act like the heterozygous type calls into question the currently accepted structure of transferrin as a monomeric protein. The greater fecundity of heterozygous females can account for the maintenance of transferrin polymorphism in pigeons.