Population Genetics: Overview

Abstract

Abstract Population genetics is concerned with the nature of, and the forces determining, the genetic composition of a population. Since any presently observed population is the outcome of an evolutionary process, the subject is in large part concerned with evolutionary questions. Indeed the evolutionary component of population genetics may be thought of as the rewriting of the Darwinian theory in terms of the Mendelian hereditary mechanism. This involves, for example, determining the rate of incorporation of favourable new alleles into a population, and the evolutionary effects of mutation. These activities are prospective , that is they discuss changes in the structure of a population forwards in time. However population genetics theory is currently largely retrospective , assessing the past history of a population (‘When and where did the most recent common ancestor of all currently living humans live?’) and investigating what forces led to the currently observed genetic composition of a population. Key Concepts: The additive genetic variance is that component of the variation in any character which is explained by ‘genes within genotypes’. The blending theory asserts that the value of any characteristic of any child is approximately the average of the corresponding characteristics in that child's parents. The correlation between relatives is the correlation in some character between close relatives (e.g. mother–daughter). The Fundamental Theorem of Natural Selection relates aspects of the change in the mean fitness of a population from one generation to the next to the parental generation additive genetic variance in fitness. The Hardy–Weinberg law shows that, in the absence of selection, genetic variation is maintained from one generation to the next. The neutral theory claim that most of presently observed genetic variation in a population, and most of the variation from one population to another, did not arise as a result of selection but arose rather as a result of purely random changes in allelic frequencies. Retrospective population genetics theory focuses on the past history of a population rather than its future evolution.