Editing Mutation rate (section)

==Background==

Different genetic variants within a species are referred to as alleles, therefore a new mutation can create a new allele. In [[population genetics]], each allele is characterized by a selection coefficient, which measures the expected change in an allele's frequency over time. The selection coefficient can either be negative, corresponding to an expected decrease, positive, corresponding to an expected increase, or zero, corresponding to no expected change. The distribution of fitness effects of new mutations is an important parameter in population genetics and has been the subject of extensive investigation.<ref name="Adam Eyre-Walker">{{cite journal | vauthors = Eyre-Walker A, Keightley PD | title = The distribution of fitness effects of new mutations | journal = Nature Reviews. Genetics | volume = 8 | issue = 8 | pages = 610–618 | date = August 2007 | pmid = 17637733 | doi = 10.1038/nrg2146 | s2cid = 10868777 }}</ref> Although measurements of this distribution have been inconsistent in the past, it is now generally thought that the majority of mutations are mildly deleterious, that many have little effect on an organism's fitness, and that a few can be favorable.

Because of [[natural selection]], unfavorable mutations will typically be eliminated from a population while favorable changes are generally kept for the next generation, and neutral changes accumulate at the rate they are created by mutations. This process happens by reproduction. In a particular generation the 'best fit' survive with higher probability, passing their genes to their offspring. The sign of the change in this probability defines mutations to be beneficial, neutral or harmful to organisms.<ref>{{cite journal | vauthors = Scally A, Durbin R | title = Revising the human mutation rate: implications for understanding human evolution | journal = Nature Reviews. Genetics | volume = 13 | issue = 10 | pages = 745–753 | date = October 2012 | pmid = 22965354 | doi = 10.1038/nrg3295 | s2cid = 18944814 }}</ref>