Editing Molecular evolution (section)

===Genetic drift===

{{Main|Genetic drift}}

Genetic drift is the change of allele frequencies from one generation to the next due to stochastic effects of [[random sampling]] in finite populations. These effects can accumulate until a mutation becomes [[Fixation (population genetics)|fixed]]  in a [[population]]. For neutral mutations, the rate of fixation per generation is equal to the mutation rate per replication. A relatively constant mutation rate thus produces a constant rate of change per generation (molecular clock).

Slightly deleterious mutations with a [[selection coefficient]] less than a threshold value of 1 / the [[effective population size]] can also fix. Many genomic features have been ascribed to accumulation of nearly neutral detrimental mutations as a result of small effective population sizes.<ref>{{cite book | vauthors = Lynch M |year=2007|title= The Origins of Genome Architecture |publisher=Sinauer|isbn=978-0-87893-484-3|author-link=Michael Lynch (geneticist)}}</ref> With a smaller effective population size, a larger variety of mutations will behave as if they are neutral due to inefficiency of selection.