Definition
What is the founder effect?
The founder effect is a kind of genetic drift that happens when a small group breaks away from a larger population and settles somewhere new, for example on an island, in an isolated valley or across a geographic barrier. The founders carry only a fraction of the original gene pool, and by chance that fraction may not match the source population. Some alleles are missing entirely, and others that were rare may be unusually common among the newcomers.
As the new population grows, it inherits the genetic makeup of those few founders, so it can stay distinct from the parent population for many generations. The idea is closely related to the bottleneck effect. The difference is that a bottleneck shrinks a population where it already lives, while a founder event starts a new population from a small sample of an old one. On islands, founder effects combined with natural selection can help new species form.
In human genetics, founder effects explain why some inherited conditions are far more frequent in particular communities. The Afrikaner population of South Africa, descended largely from a small group of Dutch settlers, has unusually high rates of Huntington disease and Fanconi anemia, and similar patterns are seen in other populations that grew from a few founders.
Word parts
Where does the term “founder effect” come from?
- found-
- to lay a foundationLatin fundare, from fundus, bottom
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Terms that go with it
- Genetic driftGenetic drift is a random change in allele frequencies from one generation to the next, caused by chance rather than by natural selection.
- Bottleneck effectThe bottleneck effect is the loss of genetic variation that follows a sudden, steep fall in population size, leaving only a few survivors to breed.
- AlleleAn allele is any of the alternative forms of a gene or DNA sequence that can occupy the same position, or locus, on a chromosome.
- SpeciationSpeciation is the evolutionary process in which one ancestral species splits into two or more species whose members can no longer interbreed.
- Gene flowGene flow is the movement of alleles from one population into another when individuals or their gametes migrate and then breed.
- Adaptive radiationAdaptive radiation is the rapid evolution of many new species from one ancestral species, each adapted to a different way of life or ecological niche.
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Written for biofideX in plain words, after checking these references:
- OpenStax Biology 2e, 19.2 Population Genetics
- NHGRI Talking Glossary: Founder Effect
- Understanding Evolution (UC Museum of Paleontology): Bottlenecks and founder effects
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