Everything about Founder Effect totally explained
In
population genetics, the
founder effect refers to the loss of genetic variation when a new colony is established by a very small number of individuals from a larger population. It was first fully outlined by
Ernst Mayr in 1952, using existing theoretical work by those such as
Sewall Wright. As a result of the loss of genetic variation, the new population may be distinctively different, both
genetically and
phenotypically, from the parent population from which it's derived. In extreme cases, the founder effect is thought to lead to the
speciation and subsequent
evolution of new species. The founder effect is a feature that can also occur in
memetic evolution.
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 even though it isn't strictly a
new population.
In addition to founder effects, the new population is often a very
small population and so shows increased sensitivity to
genetic drift, an increase in
inbreeding, and relatively low
genetic variation. This can be observed in the limited
gene pool of
Easter Islanders and those native to
Pitcairn Island.
Founder effects in island ecology
Founder populations are essential to the study of
island biogeography and
island ecology. A natural "blank slate" isn't easily found, but a classic series of studies on founder population effects were done following the catastrophic 1883 eruption of Krakatau (
Krakatoa), which erased all life on the island remnant. 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 eruption in Sumatra of about 73,000
YBP, covered some parts of India with 3–6
m of ash, and must have coated the
Nicobar Islands and
Andaman Islands, much nearer in the ash fallout cone, with life-smothering layers, restarting their biodiversity from effectively zero.
Founder effects in human populations
Due to various migrations throughout human history, founder effects are somewhat common among humans in different times and places. The effective founder population of
Quebec was only 2,600. After twelve to sixteen generations, with an eighty-fold growth but minimal gene dilution from intermarriage, Quebec has what geneticists call optimal
linkage disequilibrium (genetic sharing). The result: far fewer genetic variations, including those that have been well studied because they're connected with inheritable diseases.
Founder effects can also occur naturally as competing genetic lines die out. This means that an effective founder population consists only of those whose genetic print is identifiable in subsequent populations. Because in sexual reproduction,
genetic recombination ensures that with each generation only half the genetic material of a parent is represented in the offspring, some genetic lines may die out entirely, even though there are numerous progeny. A recent study concluded that of the people migrating across the
Bering land bridge at the close of the
ice age, only 70 left their genetic print in modern descendants, a minute effective founder population— which is easily misread as though implying that only 70 people crossed to North America. The misinterpretations of "
Mitochondrial Eve" are a case in point: it may be hard to explain that a "mitochondrial Eve" wasn't the only woman of her time.
In humans, founder effects can arise from cultural isolation, and inevitably,
endogamy. For example, the
Amish populations in the
United States, which have grown from a very few founders, have not recruited newcomers, and tend to marry within the community, exhibit founder effects. Though still rare absolutely, phenomena such as
polydactyly (extra fingers and toes, a symptom of
Ellis-van Creveld syndrome) are more common in Amish communities than in the US population at large. There is also the presence of high cases of
fumarase deficiency among the 10,000 members of the
Fundamentalist Church of Jesus Christ of Latter Day Saints community, a breakaway sect which practices both
endogamy and
polygamy, where it's estimated 75 to 80 percent of the community are blood relatives of just two men - founders
John Y. Barlow and
Joseph Smith Jessop.
Another example is the frequency of
total color-blindness among the inhabitants of
Pingelap, an island in
Micronesia. In approximately 1775, a typhoon reduced the population of the island to only 20. Among survivors, one of them was heterozygous for
achromatopsia. After few generations, the prevalence of achromatopsia is 5% of population and 30% as carriers (by comparison, in the United States, only 0.003% of population have complete achromatopsia).
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