Editing Allele frequency (section)

==Dynamics==
Population genetics describes the genetic composition of a population, including allele frequencies, and how allele frequencies are expected to change over time. The [[Hardy–Weinberg law]] describes the expected equilibrium [[genotype frequency|genotype frequencies]] in a diploid population after random mating. Random mating alone does not change allele frequencies, and the Hardy–Weinberg equilibrium assumes an infinite population size and a selectively neutral locus.<ref name="gillespie" />

In natural populations [[natural selection]] ([[adaptation]] mechanism), [[gene flow]], and [[mutation]] combine to change allele frequencies across generations. [[Genetic drift]] causes changes in allele frequency from random sampling due to offspring number variance in a finite population size, with small populations experiencing larger per generation fluctuations in frequency than large populations. There is also a theory that second adaptation mechanism exists – [[niche construction]]<ref name="Scott-Phillips">{{cite journal | last1 = Scott-Phillips | first1 = T. C. | last2 = Laland | first2 = K. N. | last3 = Shuker | first3 = D. M. | last4 = Dickins | first4 = T. E. | last5 = West | first5 = S. A. | year = 2014 | title = The Niche Construction Perspective: A Critical Appraisal | journal = Evolution | volume = 68 | issue = 5| pages = 1231–1243 | doi=10.1111/evo.12332| pmid = 24325256 | pmc = 4261998 }}</ref> According to [[extended evolutionary synthesis]] adaptation occur due to natural selection, environmental induction, non-genetic inheritance, learning and cultural transmission.<ref>{{cite journal | pmc = 4632619 | pmid=26246559 | doi=10.1098/rspb.2015.1019 | volume=282 | issue=1813 | title=The extended evolutionary synthesis: its structure, assumptions and predictions. | date=Aug 2015 | journal=Proc Biol Sci | pages=20151019| last1=Laland | first1=K. N. | last2=Uller | first2=T. | last3=Feldman | first3=M. W. | last4=Sterelny | first4=K. | last5=Müller | first5=G. B. | last6=Moczek | first6=A. | last7=Jablonka | first7=E. | last8=Odling-Smee | first8=J. }}</ref> An allele at a particular locus may also confer some fitness effect for an individual carrying that allele, on which natural selection acts. Beneficial alleles tend to increase in frequency, while deleterious alleles tend to decrease in frequency. Even when an allele is selectively neutral, selection acting on nearby genes may also change its allele frequency through [[Genetic hitchhiking|hitchhiking]] or [[background selection]].

While heterozygosity at a given locus decreases over time as alleles become fixed or lost in the population, variation is maintained in the population through new mutations and gene flow due to migration between populations. For details, see [[population genetics]].