Founder effect
In extreme cases, the founder effect is thought to lead to the speciation and subsequent evolution of new species.
[6][7] 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,[8] for instance a goat[9][10] or a human.
As the generations progress, the proportion of the haplotype that is common to all carriers of the mutation is shortened (due to genetic recombination).
The new colony may have less genetic variation than the original population, and through the random sampling of alleles during reproduction of subsequent generations, continue rapidly towards fixation.
[13] When a newly formed colony is small, its founders can strongly affect the population's genetic makeup far into the future.
[13] The variation in gene frequency between the original population and colony may also trigger the two groups to diverge significantly over the course of many generations.
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 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.
[16] 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.
[17] 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.
[18] 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.
[further explanation needed][19] Serial founder effects have occurred when populations migrate over long distances.
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.
An earlier event, the Toba eruption in Sumatra about 73,000 years ago, covered some parts of India with 3–6 m (10–20 ft) 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.
Hajji and others, and Hundertmark & Van Daele, studied the current population statuses of past founder effects in Corsican red deer and Alaskan elk, respectively.
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.
[26][27] Kolbe and others set up a pair of genetically sequenced and morphologically examined lizards 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.
In the Common Myna (Acridotheres tristis), the percentage of unique songs within a repertoire and within‐song complexity were significantly lower in birds from founder populations.
[33] 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.
Though still rare, phenomena such as polydactyly (extra fingers and toes, a symptom of a condition such as[35][36] Weyers acrodental dysostosis[35] or Ellis–Van Creveld syndrome[36]) are more common in Amish communities than in the American population at large.
[citation needed] Due in part to the founder effect,[38] however, the disease has a much higher prevalence in children of Amish, Mennonite, and Jewish descent.
[39][40] 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.
[41] In South Asia, castes like the Gujjars, the Baniyas and the Pattapu Kapu have estimated founder effects about 10 times as strong as those of Finns and Ashkenazi Jews.
As a result, complete achromatopsia has a current rate of occurrence of roughly 10%, with an additional 30% being carriers of this recessive condition.
One of the early colonists apparently carried a rare, recessive allele for retinitis pigmentosa, a progressive form of blindness that afflicts homozygous individuals.
[44] The abnormally high rate of twin births in Cândido Godói could be explained by the founder effect.
