The analysis of hidden electrophoretic variation: interspecific electrophoretic differentiation and amino acid...

In a study of 25 human variants and 23 "evolutionary alleles" of hemoglobin we show that intraspecific and interspecific patterns of electrophoretic variability are not comparable. Significant deviation from the predicted electrophoretic differentiation between evolutionary alleles is normally found only when amino acid sequence divergence exceeds 10%. When two sequences had diverged at less than 30 out of 287 amino acid residues sites, only 7% of comparisons showed significant deviations from the expected difference of electrophoretic mobility, while significant deviation was shown by 57% of comparisons involving 30-40 residue differences, by 79% in the case of 51-60 differences and by all of the comparisons involving more than 60 differences. In contrast, human variants, which differ by only one or two amino acid residues (less than 1% difference), had significant deviations in 58% of comparisons. Those mutations that appear as fixed differences in the evolutionary material probably represent only a subset of the mutations which can appear within the species. The results suggest that statistical comparisons such as genetic distance may not measure the same process within a species as between species. This is due not to inherent problems with the statistic, but rather to inherent differences in the nature of molecular changes that are detectable by electrophoresis at different stages of population divergence.