Editing Genetic drift (section)

===Rate of allele frequency change due to drift===
[[File:Random genetic drift chart.png|thumb|250px|Ten simulations of random genetic drift of a single given allele with an initial frequency distribution 0.5 measured over the course of 50 generations, repeated in three reproductively synchronous populations of different sizes. In these simulations, alleles drift to loss or fixation (frequency of 0.0 or 1.0) only in the smallest population.]]
Assuming genetic drift is the only evolutionary force acting on an allele, after ''t'' generations in many replicated populations, starting with allele frequencies of ''p'' and ''q'', the variance in allele frequency across those populations is

: <math>
V_t \approx pq\left(1-\exp\left(-\frac{t}{2N_e} \right)\right)
</math><ref>{{harvnb|Barton|Briggs|Eisen|Goldstein|2007|p=417}}</ref>