Genetic Drift

This chapter aims to investigate the evolutionary properties and significance of genetic drift. Genetic drift, like any other evolutionary force, can only operate as an evolutionary force when there is genetic variability. Genetic drift causes its most dramatic and rapid changes in small populations. The chapter consider some examples of founder and bottleneck effects. Disassortative mating can strongly interact with drift-induced linkage disequilibrium, particularly after founder or bottleneck effects. Finite population size has many important evolutionary consequences: increasing the average amount of identity-by-descent, increasing the variance of allele frequencies through time and across populations, causing the loss or fixation of alleles, and generating linkage disequilibrium. Genetic drift causes random deviations from the allele frequency of the previous generation. The variance effective size measures how rapidly allele frequencies are likely to change and/or how rapidly isolated subpopulations diverge from one another under genetic drift.