Editing Genetic drift (section)

===Moran model===

The [[Moran process|Moran model]] assumes overlapping generations. At each time step, one individual is chosen to reproduce and one individual is chosen to die. So in each timestep, the number of copies of a given allele can go up by one, go down by one, or can stay the same. This means that the [[Stochastic matrix|transition matrix]] is [[tridiagonal matrix|tridiagonal]], which means that mathematical solutions are easier for the Moran model than for the Wright–Fisher model. On the other hand, [[computer simulation]]s are usually easier to perform using the Wright–Fisher model, because fewer time steps need to be calculated. In the Moran model, it takes ''N'' timesteps to get through one generation, where ''N'' is the [[effective population size]]. In the Wright–Fisher model, it takes just one.<ref>{{Cite journal | last1 = Moran | first1 = P. A. P. | author-link = Pat Moran (statistician) | doi = 10.1017/S0305004100033193 | title = Random processes in genetics | journal = [[Mathematical Proceedings of the Cambridge Philosophical Society]]| volume = 54 |issue=1| pages = 60–71| year = 1958 | bibcode = 1958PCPS...54...60M| s2cid = 85823386 }}</ref>

In practice, the Moran and Wright–Fisher models give qualitatively similar results, but genetic drift runs twice as fast in the Moran model.