Primate hemoglobins: Polymorphisms and evolutionary patterns

Abstract

Abstract In this rrport we illustrate the apparently great incidence in the number of different kinds of electrophoretically undetectable intraspecies variants found in the course of characterizing primate hemoglobin α, β and δ sequences. Our primary interest is to assess the significance of such findings in a setting provided by fixed amino acid differences that have accumulated between species during primate evolution. Observed non-randomness in fixed mutations, with respect to both linear distribution and certain kinds of change, is interpreted as due to the restrictive effects of natural selection rather than to either differential mutability at particular positions or disturbed permutations of the genetic code in general. Thus, in the micropatterns of accumulated mutation, we adduce strong evidence for Darwinism. However, we also find that the δ chain of minor hemoglobin A2 (α2δ2)—while apparently visible to selection—seems less restricted than the β chain of the major component, hemoglobin A (α2β2). Such findings are used to support our earlier presumption that comparative changes in β and δ can serve as a model for evaluating mechanisms of amino acid replacement during evolution. We believe that equivalence between β and δ in the numbers of recognizable fixed mutations is more easily explained by non-adaptive mechanisms than by adaptive ones. The frequencies of seven different kinds of electrically neutral variants found within-species during detailed analysis of ∼70 allele products are reported here. Most, if not all, are common. We propose that the overall incidence of different kinds of electrically neutral polymorphisms is probably at least fivefold greater than the kinds of electrophoretically detectable polymorphism. In their electrical neutrality and location the electrophoretically silent polymorphisms strongly resemble the fixed mutations accumulated during evolution of primate hemoglobin chains and are thus candidates for the transient phase of non-adaptive evolution.