Founder Effect

Founder Effect

The Founder Effect is defined as a type of bottleneck, "a type of genetic drift describing the loss of the allelic variation that accompanies founding of a new population from a very small number of individuals (a small sample of a much larger source population). This effect can cause the new population to differ considerably from the source population." Examples of this showing up in human populations is polydactyly among Amish communities or the Blue people of Kentucky. Unlike bottlenecks, which persist as long as the effective population size remains

low, a founder effect is an instant event. Here is a link to a website that delves into the genomic heritage of the people of Quebec. Quebec is a community whose genomic heritage is a result of founder effects.

• The founder effect occurs when there is a lack of genetic variation due to a small mating population. The Founder Effect happens when there is a dramatic decrease in genetic diversity caused by the development of small colonies of individuals, from the original population, that remain isolated to other colonies.

• Only a small subset of the genetic diversity of the source population is likely to be

included in the new population, and the relative frequencies of these alleles may be very different from what they had been before

An example of the founder effect comes from the Afrikaner population of Dutch settlers in South Africa. This population has an abnormally high count of Huntington's Disease (nerve cells in brain degenerate) because the original Dutch settlers carried the gene with a higher frequency that the rest of the Dutch population.

• Huntington's Disease also occurs in unusually high frequency near Lake Maraciabo, Venezuela. After much research, scientists were not only able to discover the mutation that causes the devastating disease, but also trace it back to the founder herself. 200

years ago, a women had 10 children all of whom stayed in the area to raise their own children. Unfortunately, Huntington's is a dominant allele meaning that if one parent carries it, there is a 50:50 chance it will be passed to the offspring. The disease has been able to persist for so long because natural selection no longer acts after reproduction, which is when Huntington's begins to take its effects.

• Ichthyosis in golden retrievers affects 50% of the population in Europe and 30% in

America. It's an autosomal recessive disorder that causes the skin to look scalely, hence the name. Geneticists, who are searching for answers to human forms of ichthyosis, found that the disorder can be traced back to one dog. By the late 1990s/early 2000s, ichthyosis was recognized as a separate disorder from regular flaking skin. While the effects, are usually mild, it is still a major concern for breeders who are now testing their dams and sires for the ichthyosis mutation prior to breeding. Caution is being exercised, however, to not eliminate mates from the gene pool too soon because of one disorder. Doing so would result in a severe bottleneck of the golden retriever population, particularly in Europe.

•  Effect is mostly prevalent in genetic diseases. Similar with Amish, high presence of  Ellisvan- Creveld syndrome (exhibition of polydactyly - extra fingers and toes) because of marriage within community.

• The Bounty is yet another human example of the Founder Effect.