Genetic Variation and Molecular Evolution

Abstract

The comparison of DNA sequences of genes and entire genomes offers interesting insights into the possible evolutionary relatedness of genetic information of living organisms. Together with a relatively rich database from experimental microbial genetics, conclusions can be drawn on the molecular mechanisms by which genetic variations are spontaneously generated. A number of different specific mechanisms contribute to the overall mutagenesis. These mechanisms are here grouped into three natural strategies of the spontaneous generation of genetic variations: local changes of DNA sequences, intragenomic rearrangement of DNA segments, and acquisition of foreign DNA by horizontal gene transfer. These three strategies have different qualities with regard to their contributions to the evolutionary process. As a general rule, none of the known mechanisms producing genetic variants is clearly directed. Rather, the resulting alterations in the inherited genomes are more random. In addition, usually only a minority of resulting variants provide a selective advantage. Interestingly, in most of the molecular mechanisms involved, the products of so-called evolution genes are involved as generators of genetic variation and/or as modulators of the frequencies of genetic variation. Products of evolution genes work in tight collaboration with nongenetic factors such as structural flexibilities and chemical instabilities of molecules, chemical and physical mutagens, and random encounter. All of these aspects contributing to the spontaneous generation of genetic variations together form the core of the theory of molecular evolution. This theory brings neo-Darwinism to the molecular level. In view of the increasing evidence coming particularly from microbial genetics, knowledge of molecular evolution can be seen as a confirmation of Darwinism at the level of biologically active molecules, in particular, nucleic acids and proteins. Philosophical and practical implications of this knowledge will be briefly discussed.