Founder Effect
The founder effect , English founder effect , describes a genetic deviation of an isolated population or founder population (z. B. on an island) from the stock population (z. B. on the mainland). This deviation arises due to the small number of alleles present in the individuals involved in their creation and not due to different selection conditions.
This effect was described for the first time by Moritz Wagner in several treatises, which appeared in 1889 as The Origin of Species through Spatial Separation . It was mentioned under its current name by Ernst Mayr in 1942 in his work Systematics and the Origin of Species from the Viewpoint of a Zoologist .
The founder effect results in a significantly lower genotypic and phenotypic variability of the offspring, since the founder individuals usually only incompletely represent the gene pool of the parent species. This can result in reduced chances of survival in the event of extreme environmental conditions and a lack of starting material for genetic selection. Depending on the alleles present in the founder population, the population can also become more or less susceptible to purging . The founder effect can thus contribute to the easier extinction of small, isolated populations. Many of the animal and plant species that survive in the field in residual populations or that have been rescued in conservation breeding are subject to the founder effect.
The fixation probability of an allele is generally equal to its initial allele frequency . Is created z. If, for example, a new allele is mutated, this occurs once among 2N alleles in N diploid individuals. The allele frequency of the new allele is therefore 1 / (2N), and this is also the probability with which this allele will prevail. As a result, beneficial alleles may be easier to establish in small populations than in large ones.
In some cases, the founder effect can lead to the emergence of new species ( speciation ). In the breeding of pedigree dogs and pedigree cats , it can be a cause of the occurrence of breed- specific hereditary diseases .
The Galapagos finches are an example of the natural establishment of new populations . Although the islands are approx. 1000 kilometers from the South American coast, a few finches accidentally reached the Galapagos Islands in a storm about 3 million years ago. They multiplied to a founder population, which adapted here , and from which several new species have emerged through adaptive radiation .
An example of a decreasing genetic variation are the raccoons , which originally came from North America . In 1934 two individuals were released in Northern Hesse, they reproduced and founded a new rapidly growing raccoon population, the genetic variation of which, however, is significantly less than that of the American raccoons.
literature
- JW James: The founder effect and response to artificial selection. In: Genetical research Volume 16, Number 3, December 1970, pp. 241-250, ISSN 0016-6723 . PMID 5512250 .
See also
Individual evidence
- ↑ Erdmann, Ulf (ed.): Green series materials S II Evolution, Bad Sachsa, 2015, p. 26
- ↑ http://www.blackwellpublishing.com/ridley/az/Founder_effect.asp