A quantitative test of the neutral theory using pooled allozyme data.

Neutral theory predicts a positive correlation between the amount of polymorphism within species and evolutionary rate. Previous tests of this prediction using both allozyme and DNA data have led to conflicting conclusions about the influence of selection and mutation drift. It is argued here that quantitative conclusions about the adequacy of neutral theory can be obtained by analyzing genetic data pooled from many sources. Using this approach, a large database containing information on allozyme variation in over 1500 species is used to examine the relationship between heterozygosity and genetic distance. The results provide support for the hypothesis that a major percentage of protein variation can be explained by variation in neutral mutation rate, and a minor percentage by strong selection.

A study of interlocus allozyme heterozygosity correlations: implications for neutral theory.

Using a database of allozyme studies, correlations in heterozygosity between selected enzyme loci (MDH, alpha GPDH, IDH, 6PGDH, LDH, SOD, AAT, PGM, EST, PGI) were calculated across vertebrate species. Large and positive correlations were observed with untransformed heterozygosity values. However, after transformation to correct for mean species heterozygosity, correlations were substantially reduced and median values were closer to zero. Some enzymes were more often involved in significant correlations than others, and correlations calculated across species within vertebrate classes were significant for different enzyme pairs in different classes. There was no evidence that significant correlations occurred primarily between functionally related enzymes. It is suggested that the observed correlations are best explained by variation between enzyme loci in functional constraint and effective neutral mutation rate.