Editing Genetic drift (section)

===Time to loss with both drift and mutation===
The formulae above apply to an allele that is already present in a population, and which is subject to neither mutation nor natural selection. If an allele is lost by mutation much more often than it is gained by mutation, then mutation, as well as drift, may influence the time to loss. If the allele prone to mutational loss begins as fixed in the population, and is lost by mutation at rate m per replication, then the expected time in generations until its loss in a haploid population is given by

: <math>
\bar{T}_\text{lost} \approx \begin{cases}
\dfrac 1 m, \text{ if } mN_e \ll 1\\[8pt]
\dfrac{\ln{(mN_e)}+\gamma} m \text{ if } mN_e \gg 1
\end{cases}
</math>

where <math>\gamma</math> is [[Euler–Mascheroni constant|Euler's constant]].<ref>{{cite journal | vauthors = Masel J, King OD, Maughan H | title = The loss of adaptive plasticity during long periods of environmental stasis | journal = The American Naturalist | volume = 169 | issue = 1 | pages = 38–46 | date = January 2007 | pmid = 17206583 | pmc = 1766558 | doi = 10.1086/510212 | publisher = [[University of Chicago Press]] on behalf of the [[American Society of Naturalists]] | bibcode = 2007ANat..169...38M | author1-link = Joanna Masel }}</ref> The first approximation represents the waiting time until the first mutant destined for loss, with loss then occurring relatively rapidly by genetic drift, taking time {{nowrap|{{sfrac|1|''m''}} ≫ ''N''<sub>''e''</sub>.}} The second approximation represents the time needed for deterministic loss by mutation accumulation. In both cases, the time to fixation is dominated by mutation via the term {{sfrac|1|''m''}}, and is less affected by the [[effective population size]].