Editing Founder effect (section)

==General==
The founder effect is a type of [[genetic drift]], occurring when a small group in a population splinters off from the original population and forms a new one. The new colony may have less genetic variation than the original population, and through the random sampling of [[allele]]s during reproduction of subsequent generations, continue rapidly towards [[Fixation (population genetics)|fixation]]. The homozygosity increase can be calculated as <math>\Delta{f}=1/2N</math>, where <math>f</math> equals inbreeding coefficient and <math>N</math> equals population size.<ref name="Allendorf-2022">{{Cite book |last1=Allendorf |first1=Fred W. |url=https://academic.oup.com/book/41948 |title=Conservation and the Genomics of Populations |last2=Funk |first2=W. Chris |last3=Aitken |first3=Sally N. |last4=Byrne |first4=Margaret |last5=Luikart |first5=Gordon |last6=Antunes |first6=Agostinho |date=2022-02-10 |publisher=Oxford University Press |isbn=978-0-19-885656-6 |edition=3 |language=en |doi=10.1093/oso/9780198856566.001.0001}}</ref> This consequence of inbreeding makes the colony more vulnerable to extinction.<ref>{{Cite book|title=Campbell biology, AP edition|date=2011|publisher=Pearson Education/Benjamin Cummings|last=Reece|first=Jane B.|isbn=978-0-13-137504-8|edition=9th|location=Boston, MA|oclc=792861278}}</ref>
[[File:Founder effect Illustration.jpg|thumb|The small founding population experiences a loss of heterozygosity after multiple generations. ("Genetic Drift" by Boundless, 2015.<ref>{{Cite web |title=File:Founder effect Illustration.jpg - Wikipedia |url=https://commons.wikimedia.org/wiki/File:Founder_effect_Illustration.jpg |access-date=2023-03-16 |website=commons.wikimedia.org |date=13 May 2015 |language=en}}</ref>)]]
The per generation loss of heterozygosity can be calculated as <math>\Delta{h} = -1/2N</math>, where <math>h</math> equals heterozygosity.<ref name="Allendorf-2022" /> The population of the founders of the colony can also be calculated if the loss of heterozygosity from the bottleneck is known using the same equation.<ref name="Allendorf-2022" />

When a newly formed colony is small, its founders can strongly affect the population's genetic makeup far into the future. In humans, who have a slow reproduction rate, the population will remain small for many generations, effectively amplifying the drift effect generation after generation until the population reaches a certain size. The post-bottleneck population growth rate can be calculated as <math>N(t)={K \over 1+be^{rt}}</math>, where <math>t</math> equals the number of generations, <math>r</math> is the growth rate, <math>K</math> is the population equilibrium size, <math>e</math> is the natural logarithm base, and <math>b</math> is the constant <math>(K-N_0)/N_0</math>, where <math>N_0</math> is the original size of the founding colony.<ref name="Allendorf-2022" />

Alleles which were present but relatively rare in the original population can move to one of two extremes. The most common one is that the allele is soon lost altogether, but the other possibility is that the allele survives and within a few generations has become much more dispersed throughout the population. The new colony can experience an increase in the frequency of [[Dominance (genetics)|recessive]] alleles, as well, and as a result, an increased number who are [[homozygous]] for certain recessive traits.<ref name="Allendorf-2022" /> The equation to calculate reccessive allele frequencies is <math>\hat{q}=\surd N_{22}/N</math> based on [[Hardy–Weinberg principle|Hardy-Wienberg]] assumptions.<ref name="Allendorf-2022" />

The variation in gene frequency between the original population and colony may also trigger the two groups to [[genetic divergence|diverge]] significantly over the course of many generations. As the variance, or [[genetic distance]], increases, the two separated populations may become distinctively different, both [[genotype|genetically]] and [[phenotype|phenotypically]], although not only genetic drift, but also natural selection, gene flow and mutation all contribute to this divergence. This potential for relatively rapid changes in the colony's gene frequency led most scientists to consider the founder effect (and by extension, genetic drift) a significant driving force in the evolution of [[speciation|new species]]. [[Sewall Wright]] was the first to attach this significance to random drift and small, newly isolated populations with his [[shifting balance theory]] of speciation.<ref>{{cite book |last1=Wade |first1=Michael S. |last2=Wolf |first2=Jason |last3=Brodie |first3=Edmund D. |title=Epistasis and the evolutionary process |publisher=Oxford University Press |location=Oxford [Oxfordshire] |year=2000 |page=330 |isbn=978-0-19-512806-2}}</ref> Following behind Wright, [[Ernst Mayr]] created many persuasive models to show that the decline in genetic variation and small population size accompanying the founder effect were critically important for new species to develop.<ref>{{Cite book |title=Systematics and the Origin of Species: on Ernst Mayr's 100th anniversary |author1=Mayr, Ernst | author1-link=Ernst Mayr |author2=Hey, Jody |author3=Fitch, Walter M. |author4=Ayala, Francisco José |publisher=National Academies Press |year=2005 |isbn=978-0-309-09536-5 |page=367 |edition=Illustrated }}</ref> However, much less support for this view is shown today, since the hypothesis has been tested repeatedly through experimental research, and the results have been equivocal at best.{{explain|date=April 2013}} Speciation by genetic drift is a specific case of [[peripatric speciation]] which in itself occurs in rare instances.<ref>{{cite web | url=http://evolution.berkeley.edu/evosite/evo101/VC1cPeripatric.shtml | title=Peripatric Speciation | archive-url=https://web.archive.org/web/20040423015847/http://evolution.berkeley.edu/evosite/evo101/VC1cPeripatric.shtml | publisher= evolution.berkeley.edu | archive-date=April 23, 2004}}</ref> It takes place when a random change in genetic frequency of population favours the survival of a few organisms of the species with rare genes which cause reproductive mutation. These surviving organisms then breed among themselves over a long period of time to create a whole new species whose reproductive systems or behaviors are no longer compatible with the original population. {{explain|date=November 2011}}<ref>{{Cite book |title=Endless Forms |last1=Howard |first1=Daniel J. |last2=Berlocher |first2=Steward H. |publisher=Oxford University Press |isbn=978-0-19-510901-6 |page=[https://archive.org/details/endlessformsspec0000unse/page/470 470] |edition=Illustrated |location=United States |year=1998 |url=https://archive.org/details/endlessformsspec0000unse/page/470 }}</ref>