Evolution of Non-Repetitive DNA Sequences in Man and the Great Apes

Abstract

The main reason why species have diverged from each other is because mutant substitutions have accumulated and become fixed in their genomes. This has inevitably resulted in classes of DNA which are unique for each species, as well as DNA sequences which, although shared by many species, have accumulated different mutant substitutions. In this respect, a comparison of the DNA level between phylogenetically related species is a powerful tool to estimate the amount of evolutionary change which has taken place between them. These studies are based on three different properties of DNA. One is its property to denature and reaneal under experimental conditions and the possibility of separating double-stranded DNA from single-stranded DNA by hydroxylapatite binding (Britten and Kohne, 1968). Another is the possibility of forming double-stranded (heteroduplex) DNA by incubating single-stranded DNA of different species, provided there is sufficient complementarity between the DNA sequences of the species tested. A third important property is that heteroduplex DNA molecules show a lower thermal stability than reassociated DNA molecules of each of the two individual species tested (homoduplex), as a consequence of the higher amount of mismatching which inevitably occurs in heteroduplexes. Mismatching results from lack of complementarity between the DNA of the species tested, which in turn results from the number of nucleotide substitutions or replacements which have occurred in the DNA of each species after they diverged from the common ancestor.