DNA POLYMORPHISM DETECTABLE BY RESTRICTION ENDONUCLEASES

TLDR

DNA polymorphisms detected by restriction endonucleases are rapidly accumulating, and many different enzymes are needed to study phylogenetic relationships because stochastic effects are large. The study proposes several measures of DNA segment diversity within and between populations and develops statistical methods to estimate them. Statistical methods applicable to both nuclear and non‑nuclear DNA express these diversity measures in terms of mutation rate per nucleon and effective population size, and include a way to estimate nucleotide diversity from nucleon diversity. The methods demonstrate that DNA divergence between populations can be assessed by average restriction site or nucleotide differences; applied to Drosophila mtDNA, they suggest nucleotide substitution dominates evolution and provide estimates of evolutionary distances among the three species.

Abstract

ABSTRACT Data on DNA polymorphisms detected by restriction endonucleases are rapidly accumulating. With the aim of analyzing these data, several different measures of nucleon (DNA segment) diversity within and between populations are proposed, and statistical methods for estimating these quantities are developed. These statistical methods are applicable to both nuclear and non-nuclear DNAs. When evolutionary change of nucleons occurs mainly by mutation and genetic drift, all the measures can be expressed in terms of the product of mutation rate per nucleon and effective population size. A method for estimating nucleotide diversity from nucleon diversity is also presented under certain assumptions. It is shown that DNA divergence between two populations can be studied either by the average number of restriction site differences or by the average number of nucleotide differences. In either case, a large number of different restriction enzymes should be used for studying phylogenetic relationships among related organisms, since the effect of stochastic factors on these quantities is very large. The statistical methods developed have been applied to data of Shah and Langley on mitochondrial (mt)DNA from Drosophila melanogaster, simulans and virilis. This application has suggested that the evolutionary change of mtDNA in higher animals occurs mainly by nucleotide substitution rather than by deletion and insertion. The evolutionary distances among the three species have also been estimated.