Chapter 9 - Nonmolecular Evolutionary Genetics

Abstract

Nonmolecular evolutionary genetics concerns only the level of the allele and studies how alleles might replace other alleles over time. It is believed that the changes in genetic makeup are due to mutations. Two possible means by which mutations can result in changes in alleles and allele relative frequencies in a population---namely, natural selection and genetic drift---are discussed. Natural selection can result in an increase in the relative frequencies of alleles that impart to the individual these favorable traits. The process of the change in allele relative frequencies due only to chance is called genetic drift. This chapter investigates ways in which allele relative frequencies might change if neither of them occurred. It analyzes allele relative frequency changes due to natural selection and shows how genetic drift can account for changes in the relative frequencies of alleles. Further, it presents results obtained when it is assumed that natural selection and genetic drift are acting simultaneously. Finally, the rate of substitution is discussed and is shown that new alleles due to advantageous mutations become fixed in the population far more often than new alleles due to neutral mutations.