View source for Founder effect

{{short description|Effect in population genetics}}
{{for|the concept in organizations|Founder's syndrome}}
[[File:Founder effect.svg|thumb|upright=1.5|Founder effect: The original population (left) could give rise to different founder populations (right).]]

In [[population genetics]], the '''founder effect''' is the loss of [[genetic variation]] that occurs when a new [[population]] is established by a very small number of individuals from a larger population. It was first fully outlined by [[Ernst Mayr]] in 1942,<ref>{{cite journal |pmid=15280221 |pmc=1470966 |url=http://www.genetics.org/cgi/pmidlookup?view=long&pmid=15280221 |year=2004 |last1=Provine |first1=W. B. |author-link=Will Provine |title=Ernst Mayr: Genetics and speciation |journal=Genetics |volume=167 |issue=3 |pages=1041–6 |doi=10.1093/genetics/167.3.1041 }}</ref> using existing theoretical work by those such as [[Sewall Wright]].<ref>{{cite journal |pmid=6777243 |pmc=1214177 |url=http://www.genetics.org/cgi/pmidlookup?view=long&pmid=6777243 |year=1980 |last1=Templeton |first1=A. R. |title=The theory of speciation via the founder principle |journal=Genetics |volume=94 |issue=4 |pages=1011–38 |doi=10.1093/genetics/94.4.1011 }}</ref> As a result of the loss of genetic variation, the new population may be distinctively different, both [[genotype|genotypically]] and [[phenotype|phenotypically]], from the parent population from which it is derived. In extreme cases, the founder effect is thought to lead to the [[speciation]] and subsequent [[evolution]] of new species.<ref>{{cite journal | vauthors = Joly E | title = The existence of species rests on a metastable equilibrium between inbreeding and outbreeding. An essay on the close relationship between speciation, inbreeding and recessive mutations | journal = Biology Direct | volume = 6 | pages = 62 | date = December 2011 | pmid = 22152499 | pmc = 3275546 | doi = 10.1186/1745-6150-6-62 | doi-access = free }}</ref>

In the figure shown, the original population has nearly equal numbers of blue and red individuals. The three smaller founder populations show that one or the other color may predominate (founder effect), due to random sampling  of the original population. A [[population bottleneck]] may also cause a founder effect, though it is not strictly a new population.

The founder effect occurs when a small group of migrants—not genetically representative of the population from which they came—establish in a new area.<ref>{{cite book |first1=Leland |last1=Hartwell |first2=Leroy |last2=Hood |first3=Michael |last3=Goldberg |first4=Ann E. |last4=Reynolds |first5=Lee |last5=Silver |first6=Ruth C |last6=Veres |year=2004 |title=Genetics: From Genes to Genomes |url=https://archive.org/details/genetics00 |url-access=registration |page=[https://archive.org/details/genetics00/page/241 241] |publisher=McGraw-Hill Higher Education |isbn=978-0-07-121468-1}}</ref><ref>{{cite book |first1=Peter H. |last1=Raven |first2=Ray F. |last2=Evert |first3=Susan E. |last3=Eichhorn |year=1999 |title=Biology of Plants |page=241 |publisher=W H Freeman and Company}}</ref> In addition to founder effects, the new population is often [[small population size|very small]], so it shows increased sensitivity to [[genetic drift]], an increase in [[inbreeding]], and relatively low [[genetic variation]].

==Founder mutation==
In [[genetics]], a '''founder mutation''' is a [[mutation]] that appears in the [[DNA]] of one or more individuals which are founders of a distinct population. Founder mutations initiate with changes that occur in the DNA and can be passed down to other generations.<ref name=BSCS>{{cite web |url=http://bscs.org/pages/curriculumdevelopment/onco/glossary.htm |title=Bioinformatics Glossary |publisher=bscs.org |access-date=2009-03-23 |url-status=dead |archive-url=https://web.archive.org/web/20090325145659/http://bscs.org/pages/curriculumdevelopment/onco/glossary.htm |archive-date=March 25, 2009 }}</ref><ref name=CIHR>{{cite web|url=http://www.mshri.on.ca/colorectalcancer/definitions.html |title=Colorectal Cancer Research Definitions |publisher=www.mshri.on.ca |access-date=2009-03-23 |url-status=dead |archive-url=https://web.archive.org/web/20090724072927/http://www.mshri.on.ca/colorectalcancer/definitions.html |archive-date=July 24, 2009 }}</ref> Any organism—from a simple virus to something complex like a mammal—whose progeny carry its mutation has the potential to express the founder effect,<ref name="pmid26052661">{{cite journal |author1=Joseph, S. B. |author2=Swanstrom, R. |author3=Kashuba, A. D. |author4=Cohen, M. S.  | title=Bottlenecks in HIV-1 transmission: insights from the study of founder viruses | journal=[[Nature Reviews Microbiology]] | volume=13 | issue=7 | pages=414–425 | year=2015 | doi=10.1038/nrmicro3471 | pmc=4793885 | pmid=26052661 }}</ref> for instance a goat<ref name="pmid23516474">{{cite journal |author1=Cooper, C. A. |author2=Garas Klobas, L. C. |author3=Maga, E. A. |author4=Murray, J. D.  | title=Consuming transgenic goats' milk containing the antimicrobial protein lysozyme helps resolve diarrhea in young pigs | journal=[[PLOS ONE]] | volume=8 | issue=3 | pages=e58409 | year=2013 | pmc=3596375 | doi=10.1371/journal.pone.0058409 | pmid=23516474 | bibcode=2013PLoSO...858409C |doi-access=free }}</ref><ref>{{cite web | last=Molteni | first=Megan | title=Spilled Milk | date=June 30, 2016 | url=http://undark.org/article/gmo-goats-lysozyme-uc-davis-diarrhea/ | access-date=2017-01-12 }}</ref> or a human.<ref name="pmid27286788">{{cite journal |author1=Ossa, C. A. |author2=Torres, D.  | title=Founder and Recurrent Mutations in BRCA1 and BRCA2 Genes in Latin American Countries: State of the Art and Literature Review | journal=The Oncologist | volume=21 | issue=7 | pages=832–839 | year=2016 | doi=10.1634/theoncologist.2015-0416 | pmid=27286788 | pmc=4943386}}</ref>

Founder mutations originate in long stretches of DNA on a single [[chromosome]]; indeed, the original [[haplotype]] is the whole chromosome. As the generations progress, the proportion of the haplotype that is common to all carriers of the mutation is shortened (due to [[genetic recombination]]). This shortening allows scientists to roughly estimate the age of the mutation.<ref name=SCIAM>{{cite journal |title=Founder Mutations: Scientific American
|journal=Scientific American
|volume=293
|issue=4
|pages=78–85
|doi=10.1038/scientificamerican1005-78
|pmid = 16196257|year=2005
|last1=Drayna
|first1=Dennis
}}</ref>

==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>

==Serial founder effect==
Serial founder effects have occurred when populations migrate over long distances. Such long-distance migrations typically involve relatively rapid movements followed by periods of settlement. The populations in each migration carry only a subset of the genetic diversity carried from previous migrations. As a result, genetic differentiation tends to increase with geographic distance as described by the "isolation by distance" model.<ref>{{cite journal |doi=10.1073/pnas.0507611102 |jstor=4143304 |pmid=16243969 |pmc=1276087 |title=Support from the relationship of genetic and geographic distance in human populations for a serial founder effect originating in Africa |journal=Proceedings of the National Academy of Sciences |volume=102 |issue=44 |pages=15942–7 |year=2005 |last1=Ramachandran |first1=S. |last2=Deshpande |first2=O. |last3=Roseman |first3=C. C. |last4=Rosenberg |first4=N. A. |last5=Feldman |first5=M. W. |last6=Cavalli-Sforza |first6=L. L. |bibcode=2005PNAS..10215942R |doi-access=free }}</ref> The migration of humans [[Recent African origin of modern humans|out of Africa]] is characterized by serial founder effects.<ref>{{cite journal |doi=10.1073/pnas.0903341106 |jstor=40485019 |pmid=19706453 |pmc=2752555 |title=Explaining worldwide patterns of human genetic variation using a coalescent-based serial founder model of migration outward from Africa |journal=Proceedings of the National Academy of Sciences |volume=106 |issue=38 |pages=16057–62 |year=2009 |last1=Degiorgio |first1=M. |last2=Jakobsson |first2=M. |last3=Rosenberg |first3=N. A. |bibcode=2009PNAS..10616057D |doi-access=free }}</ref> Africa has the highest degree of human genetic diversity of any continent, which is consistent with an African origin of modern humans.<ref>{{Cite journal |last1=Schlebusch |first1=Carina M. |last2=Jakobsson |first2=Mattias |date=2018-08-31 |title=Tales of Human Migration, Admixture, and Selection in Africa |journal=Annual Review of Genomics and Human Genetics |language=en |volume=19 |issue=1 |pages=405–428 |doi=10.1146/annurev-genom-083117-021759 |issn=1527-8204|doi-access=free |pmid=29727585 }}</ref>

==In island ecology==
Founder populations are essential to the study of [[island biogeography]] and [[island ecology]]. A natural "blank slate" is not easily found, but a classic series of studies on founder population effects was done following the catastrophic [[1883 eruption of Krakatoa]], which erased all life on the island.<ref>{{Cite journal |last=Treub |first=Melchior |date=1888 |title=Notice sur la nouvelle flore de Krakatau |url=https://www.biodiversitylibrary.org/item/24955#page/229/mode/1up |journal=Annales du Jardin botanique de Buitenzorg |volume=7 |pages=213–223 |via=Biodiversity Heritage Library}}</ref><ref>{{Cite journal |last=Bordage |first=Edmond |date=1916 |title=Le repeuplement végétal et animal des îles Krakatoa depuis l'éruption de 1883 |url=https://www.persee.fr/doc/geo_0003-4010_1916_num_25_133_8848 |journal=Annales de géographie |volume=25 |issue=133 |pages=1–22 |doi=10.3406/geo.1916.8848}}</ref> Another continuing study has been following the biocolonization of [[Surtsey]], [[Iceland]], a new volcanic island that erupted offshore between 1963 and 1967. An earlier event, the [[Toba catastrophe theory|Toba eruption]] in Sumatra about 73,000 years ago, covered some parts of India with {{convert|3|-|6|m|0|abbr=on}} of ash, and must have coated the [[Nicobar Islands]] and [[Andaman Islands]], much nearer in the ash fallout cone, with life-smothering layers, forcing the restart of their [[biodiversity]].<ref>{{Cite journal|last1=O’Connell|first1=Kyle A.|last2=Oaks|first2=Jamie R.|last3=Hamidy|first3=Amir|last4=Shaney|first4=Kyle J.|last5=Kurniawan|first5=Nia|last6=Smith|first6=Eric N.|last7=Fujita|first7=Matthew K.|date=August 2020|title=Impacts of the Toba eruption and montane forest expansion on diversification in Sumatran parachuting frogs ( Rhacophorus )|url=https://onlinelibrary.wiley.com/doi/10.1111/mec.15541|journal=Molecular Ecology|language=en|volume=29|issue=16|pages=2994–3009|doi=10.1111/mec.15541|pmid=32633832 |bibcode=2020MolEc..29.2994O |s2cid=220384153 |issn=0962-1083}}</ref>

However, not all founder effect studies are initiated after a natural disaster; some scientists study the reinstatement of a species that became locally extinct or hadn't existed there before. A study has been in place since 1958 studying the wolf/moose interaction on [[Wolves and moose on Isle Royale|Isle Royale]] in Lake Superior after those animals naturally migrated there, perhaps on winter ice. Hajji and others, and Hundertmark & Van Daele, studied the current population statuses of past founder effects in [[Corsican red deer]] and Alaskan elk, respectively. Corsican red deer are still listed as an [[endangered species]], decades after a severe bottleneck. They inhabit the Tyrrhenian islands and surrounding mainlands currently, and before the bottleneck, but Hajji and others wanted to know how the deer originally got to the islands, and from what parent population or species they were derived. Through molecular analysis, they were able to determine a possible lineage, with red deer from the islands of [[Corsica]] and [[Sardinia]] being the most related to one another. These results are promising, as the island of Corsica was repopulated with red deer from the Sardinian island after the original Corsican red deer population became extinct, and the deer now inhabiting the island of Corsica are diverging from those inhabiting Sardinia.<ref>{{cite journal |doi=10.1007/s10531-007-9297-9 |title=Phylogeography and founder effect of the endangered Corsican red deer (Cervus elaphus corsicanus) |journal=Biodiversity and Conservation |volume=17 |issue=3 |pages=659–73 |year=2007 |last1=Hajji |first1=Ghaiet M. |last2=Charfi-Cheikrouha |first2=F. |last3=Lorenzini |first3=Rita |last4=Vigne |first4=Jean-Denis |last5=Hartl |first5=Günther B. |last6=Zachos |first6=Frank E. |s2cid=26357327 }}</ref><ref>{{cite journal |doi=10.1007/s10592-009-0013-z |title=Founder effect and bottleneck signatures in an introduced, insular population of elk |journal=Conservation Genetics |volume=11 |pages=139–47 |year=2009 |last1=Hundertmark |first1=Kris J. |last2=Van Daele |first2=Larry J. |s2cid=24280253 }}</ref>

Kolbe and others set up a pair of genetically sequenced and morphologically examined [[lizard]]s on seven small islands to watch each new population's growth and adaptation to its new environment. Specifically, they were looking at the effects on limb length and perch width, both widely varying phenotypic ranges in the parent population. Unfortunately, immigration did occur, but the founder effect and adaptive differentiation, which could eventually lead to peripatric speciation, were statistically and biologically significant between the island populations after a few years. The authors also point out that although adaptive differentiation is significant, the differences between island populations best reflect the differences between founders and their genetic diversity that has been passed down through the generations.<ref>{{cite journal |doi=10.1126/science.1209566 |pmid=22300849 |title=Founder Effects Persist Despite Adaptive Differentiation: A Field Experiment with Lizards |journal=Science |volume=335 |issue=6072 |pages=1086–9 |year=2012 |last1=Kolbe |first1=J. J. |last2=Leal |first2=M. |last3=Schoener |first3=T. W. |last4=Spiller |first4=D. A. |last5=Losos |first5=J. B. |bibcode=2012Sci...335.1086K |citeseerx=10.1.1.363.77 |s2cid=12374679 }}</ref>

Founder effects can affect complex traits, such as song diversity. In the [[Common myna|Common Myna]] (''Acridotheres tristis''), the percentage of unique songs within a repertoire and within‐song complexity were significantly lower in birds from founder populations.<ref>{{Cite journal|last1=Hill|first1=Samuel D.|last2=Pawley|first2=Matthew D. M.|date=2019|title=Reduced song complexity in founder populations of a widely distributed songbird|journal=Ibis|language=en|volume=161|issue=2|pages=435–440|doi=10.1111/ibi.12692|s2cid=92000651|issn=1474-919X}}</ref>

It was found by Tarr et al. (1998) that the loss of heterozygosity of the [[Laysan finch]] (''Telespiza cantans'') after founding events on small islands in the Pacific Ocean closely matched theoretical calculations upon examination of [[microsatellite]] loci.<ref>{{Cite journal |last1=Tarr |first1=C. L. |last2=Conant |first2=S. |last3=Fleischer |first3=R. C. |date=1998 |title=Founder events and variation at microsatellite loci in an insular passerine bird, the Laysan finch ( Telespiza cantans ) |journal=Molecular Ecology |language=en |volume=7 |issue=6 |pages=719–731 |doi=10.1046/j.1365-294x.1998.00385.x|doi-access=free |bibcode=1998MolEc...7..719T }}</ref>

==Among human populations==
Genetic studies of founder effect have concentrated on discovering ancestral and novel genetic diseases caused by founder effect and, to a lesser degree, on ancestry-related founder effects on populations, races, and ancient migrations, as well other aspects. The founder population could be the common ancestry of race or ethnicity or the forced localizations caused by artificial countries inside the larger group of ancestry, hence causing an original founder effect.{{clarify|date=March 2024}} Race and specific founder effect mutation diseases are found in all races or ethnicities,{{citation needed|date=March 2024}} and country-specific mutation diseases are caused by increasing [[homozygosity]] (the existence of same gene on both chromosomes pairs, hence a recessive disease may increase in just few generations). The genetic abnormality will increase incrementally with the decrease of number of isolated populations making tribe-specific diseases (such as [[Ashkenazi Jews]], [[Amish]], and [[Bedouin]]s) and novel genetic defects.<ref>{{cite book |title=Emery and Rimoin's Principles and Practice of Medical Genetics and Genomics|date=2020 |chapter=founder effect |url=https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/founder-effect#:~:text=The%20founder%20effect%20refers%20to,number%20of%20that%20founder%27s%20offspring|edition=Seventh}}</ref>
In recessive diseases, founder populations where underlying levels of genome-wide homozygosity are high due to shared common ancestry, but also for consanguineous populations that will have large genome-wide homozygous regions due to inbreeding. Having a catalog of disease-associated variation in these populations enables rapid, early, and accurate diagnoses that may improve patient outcomes due to informed clinical management and early interventions. Enclosed communities such as Amish communities, Ashkenazi communities, and relatively isolated islands allow scientists to better understand and further discover the mutated genes that cause these rare diseases and allow them to also discover protective genes as well.<ref>{{ cite book|chapter=Recessive diseases and founder genetics|last=Puffenberger|first=Erik|title=Genomics of Rare Diseases|date=2021}}</ref>

Due to various migrations throughout human history, founder effects are somewhat common among humans in different times and places. The [[French Canadians]] of [[Quebec]] are a classical example of founder population. Over 150 years of French colonization, between 1608 and 1760, an estimated 8,500 pioneers married and left at least one descendant on the territory.<ref>{{cite book |first1=Hubert |last1=Charbonneau |first2=Bertrand |last2=Desjardins |first3=Jacques |last3=Légaré |first4=Hubert |last4=Denis |chapter=The Population of the St. Lawrence Valley 1608–1760 |chapter-url=https://books.google.com/books?id=BPdgiysIVcgC&pg=PA99 |pages=99–142 |editor1-first=Michael R. |editor1-last=Haines |editor2-first=Richard H. |editor2-last=Stecke |year=2010 |title=A Population History of North America |publisher=Cambridge University Press |isbn=978-0-521-49666-7}}</ref> Following the takeover of the colony by the British crown in 1760, immigration from France effectively stopped, but descendants of French settlers continued to grow in number mainly due to their high fertility rate. Intermarriage occurred mostly with the deported [[Acadians]] and migrants coming from the British Isles. Since the 20th century, immigration in Quebec and mixing of French Canadians involve people from all over the world. While the French Canadians of Quebec today may be partly of other ancestries, the genetic contribution of the original French founders is predominant, explaining about 90% of regional gene pools, while Acadian (descended from other French settlers in eastern Canada) admixtures contributing 4% British and 2% Native American and other groups contributing less.<ref>{{cite journal |doi=10.1002/ajpa.21424 |pmid=21302269 |title=Admixed ancestry and stratification of Quebec regional populations |journal=American Journal of Physical Anthropology |volume=144 |issue=3 |pages=432–41 |year=2011 |last1=Bherer |first1=Claude |last2=Labuda |first2=Damian |last3=Roy-Gagnon |first3=Marie-Hélène |last4=Houde |first4=Louis |last5=Tremblay |first5=Marc |last6=Vézina |first6=Hélène |url=https://constellation.uqac.ca/id/eprint/8289/1/8289.pdf }}</ref>

In humans, founder effects can arise from cultural isolation, and inevitably, [[endogamy]]. For example, the Amish populations in the United States exhibit founder effects because they have grown from a very few founders, have not recruited newcomers, and tend to marry within the community. Though still rare, phenomena such as [[polydactyly]] (extra fingers and toes, a symptom of a condition such as<ref name="ghr-nlm-nih-WAD">{{cite web | url =https://ghr.nlm.nih.gov/condition/weyers-acrofacial-dysostosis
| title =Weyers acrofacial dysostosis / "Genetics Home Reference" ("Your Guide to Understanding Genetic Conditions"), from the "US National Library of Medicine" | publisher =[[National Library of Medicine]] (NLM), which is part of the [[National Institutes of Health]], an agency of the [[U.S. Department of Health and Human Services]] ... ((Note: archived from [[an earlier version of]] the original.))| date =July 18, 2017 | access-date =July 24, 2017 | url-status =live | archive-url =https://web.archive.org/web/20170627181019/https://ghr.nlm.nih.gov/condition/weyers-acrofacial-dysostosis| archive-date =June 27, 2017 | quote =People with Weyers acrofacial dysostosis have abnormally small or malformed fingernails and toenails. Most people with the condition are relatively short, and they may have extra fingers or toes (polydactyly). [...] The features of Weyers acrofacial dysostosis overlap with those of another, more severe condition called [[Ellis–Van Creveld syndrome]]. In addition to tooth and nail abnormalities, people with Ellis-van Creveld syndrome have very short stature and are often born with heart defects. The two conditions are caused by mutations in the same genes.}}</ref><ref name="ghr-nlm-nih-naming">{{cite web | url =https://ghr.nlm.nih.gov/primer/mutationsanddisorders/naming | title =How are genetic conditions and genes named? / "Genetics Home Reference" ("Your Guide to Understanding Genetic Conditions"), from the "US National Library of Medicine" | publisher =[[National Library of Medicine]] (NLM), which is part of the [[National Institutes of Health]], an agency of the [[U.S. Department of Health and Human Services]] ... ((Note: archived from [[an earlier version of]] the original.)) | date =July 18, 2017 | access-date =July 24, 2017 | url-status =live | archive-url =https://web.archive.org/web/20170709220018/https://ghr.nlm.nih.gov/primer/mutationsanddisorders/naming | archive-date =July 9, 2017 }}</ref> [[Weyers acrodental dysostosis]]<ref name="ghr-nlm-nih-WAD"/> or [[Ellis–Van Creveld syndrome]]<ref name="ghr-nlm-nih-naming"/>) are more common in Amish communities than in the American population at large.<ref>{{cite journal |pmid=14217223 |year=1964 |last1=McKusick |first1=V. A. |title=Dwarfism in the Amish I. The Ellis-Van Creveld Syndrome |journal=Bulletin of the Johns Hopkins Hospital |volume=115 |pages=306–36 |last2=Egeland |first2=J. A. |last3=Eldridge |first3=R |last4=Krusen |first4=D. E. }}</ref> [[Maple syrup urine disease]] affects about one out of 180,000 infants in the general population.{{citation needed|date=April 2023}} Due in part to the founder effect,<ref name="fe">{{cite journal |pmid=2706837 |year=1989 |last1=Jaworski |first1=M. A. |title=Genetic conditions among Canadian Mennonites: Evidence for a founder effect among the old colony (Chortitza) Mennonites |journal=Clinical and Investigative Medicine |volume=12 |issue=2 |pages=127–41 |last2=Severini |first2=A |last3=Mansour |first3=G |last4=Konrad |first4=H. M. |last5=Slater |first5=J |last6=Hennig |first6=K |last7=Schlaut |first7=J |last8=Yoon |first8=J. W. |last9=Pak |first9=C. Y. |last10=MacLaren |first10=N }}</ref> however, the disease has a much higher prevalence in children of Amish, [[Mennonite]], and [[Jewish]] descent.<ref name="msudmp">{{cite journal |doi=10.1002/ajmg.c.20003 |pmid=12888983 |title=Genetic heritage of the Old Order Mennonites of southeastern Pennsylvania |journal=American Journal of Medical Genetics |volume=121C |issue=1 |pages=18–31 |year=2003 |last1=Puffenberger |first1=E.G. |s2cid=25317649 |doi-access=free }}</ref><ref name="msudaj">{{Cite web | url=http://www.mazornet.com/genetics/MapleSyrup.htm | title=Maple Syrup Urine Disease (MSUD) - Jewish Genetic Disease}}</ref> Similarly, a high frequency of [[fumarase deficiency]] exists among the 10,000 members of the [[Fundamentalist Church of Jesus Christ of Latter Day Saints]], a community which practices both [[endogamy]] and [[polygyny]], where an estimated 75–80% of the community are blood relatives of just two men—founders [[John Y. Barlow]] and [[Joseph Smith Jessop]].<ref name="Dougherty2005">[https://web.archive.org/web/20070311041742/http://www.phoenixnewtimes.com/2005-12-29/news/forbidden-fruit/ Forbidden Fruit:Inbreeding among polygamists along the Arizona-Utah border is producing a caste of severely retarded and deformed children], by John Dougherty, ''The Phoenix New Times News'', December 29, 2005, page 2.</ref> In South Asia, castes like the [[Gurjar|Gujjars]], the [[Bania (caste)|Baniyas]] and the Pattapu Kapu have estimated founder effects about 10 times as strong as those of [[Finns]] and [[Ashkenazi Jews]].<ref>{{Cite news|last=Yin|first=Steph|url=https://www.nytimes.com/2017/07/17/health/india-south-asia-castes-genetics-diseases.html|title=In South Asian Social Castes, a Living Lab for Genetic Disease|date=2017-07-17|work=The New York Times|access-date=2020-03-13|language=en-US|issn=0362-4331}}</ref>

In Africa, many members of the [[Vadoma]] tribe inherit [[ectrodactyly]], giving them the nickname of the "two-toed tribe".<ref name="Farrell">{{cite journal |author=Farrell HB |title=The two-toed Wadoma--familial ectrodactyly in Zimbabwe |journal=S. Afr. Med. J. |volume=65 |issue=13 |pages=531–3 |year=1984 |pmid=6710256 }}</ref>{{Failed verification|date=October 2022}}

The island of [[Pingelap]] also suffered a population bottleneck in 1775 following a typhoon that had reduced the population to only 20 people. As a result, complete [[achromatopsia]] has a current rate of occurrence of roughly 10%, with an additional 30% being carriers of this recessive condition.

Around 1814, a small group of British colonists founded a settlement on [[Tristan da Cunha]], a group of small islands in the Atlantic Ocean, midway between Africa and South America. One of the early colonists apparently carried a rare, recessive allele for [[retinitis pigmentosa]], a progressive form of blindness that afflicts [[homozygous]] individuals. As late as 1961, the majority of the genes in the gene pool on Tristan were still derived from 15 original ancestors; as a consequence of the inbreeding, of 232 people tested in 1961, four were suffering from retinitis pigmentosa. This represents a prevalence of 1 in 58, compared with a worldwide prevalence of around 1 in 4,000.<ref>{{cite journal | pmc=2906351 | pmid=4864588 | volume=59 |issue = 2| title=Genetical changes in mice and men | year=1967 | journal=Eugen Rev | pages=78–96 | last1=Berry | first1=RJ}}</ref>

The abnormally high rate of twin births in [[Cândido Godói]] could be explained by the founder effect.<ref>{{cite journal |doi=10.1111/ahg.12001 |pmid=23369099 |title=So Close, So Far Away: Analysis of Surnames in a Town of Twins (Cândido Godói, Brazil) |journal=Annals of Human Genetics |volume=77 |issue=2 |pages=125–36 |year=2013 |last1=De Oliveira |first1=Marcelo Zagonel |last2=Schüler-Faccini |first2=Lavínia |last3=Demarchi |first3=Dario A. |last4=Alfaro |first4=Emma L. |last5=Dipierri |first5=José E. |last6=Veronez |first6=Mauricio R. |last7=Colling Cassel |first7=Marlise |last8=Tagliani-Ribeiro |first8=Alice |last9=Silveira Matte |first9=Ursula |last10=Ramallo |first10=Virginia |s2cid=206980257 |hdl=11336/11007 |hdl-access=free }}</ref>

On 31 August 2023, researchers reported, based on genetic studies, that a [[human ancestor]] [[population bottleneck]] (from a possible 100,000 to 1000 individuals) occurred "around 930,000 and 813,000 years ago ... lasted for about 117,000 years and brought human ancestors close to extinction."<ref name="NYT-20230831">{{cite news |last=Zimmer |first=Carl |authorlink=Carl Zimmer |title=Humanity's Ancestors Nearly Died Out, Genetic Study Suggests - The population crashed following climate change about 930,000 years ago, scientists concluded. Other experts aren't convinced by the analysis. |url=https://www.nytimes.com/2023/08/31/science/human-survival-bottleneck.html |date=31 August 2023 |work=[[the New York Times]] |url-status=live |archiveurl= https://archive.today/20230831182259/https://www.nytimes.com/2023/08/31/science/human-survival-bottleneck.html |archivedate=31 August 2023 |accessdate=2 September 2023 }}</ref><ref name="SCI-20230831">{{cite journal |author=Hu, Wangjie |display-authors=et al. |title=Genomic inference of a severe human bottleneck during the Early to Middle Pleistocene transition |url=http://www.science.org/doi/10.1126/science.abq7487 |date=31 August 2023 |journal=[[Science (journal)|Science]] |volume=381 |issue=6661 |pages=979–984 |doi=10.1126/science.abq7487 |pmid=37651513 |bibcode=2023Sci...381..979H |url-status=live |archiveurl=https://archive.today/20230901024052/https://www.science.org/doi/10.1126/science.abq7487 |archivedate=1 September 2023 |accessdate=2 September 2023 }}</ref>

==See also==
{{Div col|colwidth=20em}}
* [[Cousin marriage]]
* [[Founder takes all]]
* [[Genetic bottleneck]]
* [[Genetic drift]]
* [[Inbreeding depression]]
* [[Mitochondrial Eve]]
* [[Neolithic founder crops]]
* [[Persister cells]]
* [[Popular sire effect]]
* [[Small population size]]
{{Div col end}}

==References==
{{Reflist|30em}}

== Further reading ==
* {{Cite book|last=Mayr|first=Ernst|author-link=Ernst Mayr|year=1954|chapter=Change of genetic environment and evolution|editor=Julian Huxley|title=Evolution as a Process|publisher=George Allen & Unwin|location=London|oclc=974739}}
* {{cite book|last=Mayr|first=Ernst|title=Animal Species and Evolution|url=https://archive.org/details/animalspeciesevo00mayr|url-access=registration|publisher=Belknap Press of Harvard University Press|location=Cambridge|year=1963|isbn=978-0-674-03750-2}}

==External links==
{{Commons category}}
* [http://www.blackwellpublishing.com/ridley/a-z/Founder_effect.asp Founder effect]

{{Population genetics}}
{{authority control}}

[[Category:Ecology]]
[[Category:Evolutionary biology]]
[[Category:Mutation]]
[[Category:Population genetics]]