Observed relationships between protein heterozygosity and protein genetic distance and comparisons with neutral expectations

Abstract

SummaryRelationships between protein genetic distance (D) and protein heterozygosity (H) were studied using allele frequency data for 42 proteins derived from multilocus electrophoretic surveys of genetic variation in over 200 invertebrate and over 300 vertebrate species.D¯andH¯values for the different proteins (mostly enzymes) were calculated, and large and significant correlations betweenD¯andH¯were found in comparisons of both intraspecific and interspecific populations. Empirical relationships betweenD¯andH¯were compared with neutral expectations under the stepwise model of neutral mutation with the assumption that populations are in equilibrium with respect to the effects of mutation and genetic drift.At low divergence levels, a linear relationship ofD¯onH¯was observed, but at high levels of divergenceDtended towards an asymptote at highH¯. The results at high divergence cannot be explained using the approximate relationshipD=2ut(whereu= mutation rate,t= time). However, computer simulations of neutral models showed that changes of this nature in the relationship betweenD¯andH¯were to be expected as divergence increases, the equationD=2utbeing a poor approximation at highDWe therefore conclude that the observed relationships betweenD¯andH¯are, in fact, compatible with equilibrium neutral theory.