Estimation of evolutionary distances between homologous nucleotide sequences.

Abstract

By using 2 models of evolutionary base substitutions (three-substitution-type and two-frequency-class models) some formulae are derived which permit a simple estimation of the evolutionary distances (and also the evolutionary rates when the divergence times are known) through comparative studies of DNA (and RNA) sequences. These formulae are applied to estimate the base substitution rates at the 1st, 2nd and 3rd positions of codons in genes for presomatotropins, preproinsulins and .alpha.- and .beta.-globins (using comparisons involving mammals). Formulae for estimating the synonymous component at the 3rd codon position and the standard errors are obtained. The rates of synonymous base substitutions not only are very high, but also are roughly equal to each other between genes, even when amino acid-altering substitution rates are quite different; this is consistent with the neutral mutation-random drift hypothesis of molecular evolution.