Mechanisms Of Evolutionary Change: The Founder Effect

The Founder Effect

Founder Effect: As definite as they may seem, some biological processes could occur randomly. In fact, the evolution of some species of living organisms is believed to arise from such.

Several theories have argued about changes that occur in gene frequencies that trigger the generation of some species.

For instance, one particular principle was proposed and scientific-wise, it serves as a strong force in the origin of species: Founder effect.

Previously, we had explored the chromosomal mutations and Autosomal Recessive Inheritance. In this article, we’ll explore the principles of Founder effect, how it impacts existing living organisms, and several recorded examples of it.

What is Founder Effect?

By definition, Founder effect[1] is the loss of genetic variation that occurs when a small group of individuals is separated from a larger group and then establishes a new population. Originally, Founder effect was proposed in order to explain the origin of islands located in high elevations. Now, it serve as an event to justify the origins of species.

  • The Founder effect is considered as a sub-type of Bottleneck effect[2] , which is defined as the loss of the variation in the alleles after the founding of a new population from the main population. But unlike bottlenecks that last until the population is small, Founder effect is just an instant event.
  • The alleles present in the new population may not necessarily reflect those of the larger population. And the more that the new population grows; it becomes more and more distinct from the original one.
  • The chances of passing on the gene increase more when the individuals in the new population tend to mate within and interbreed.

A good illustration of this phenomenon can be seen below here:

Founder Effect: History & Origin

During the 1940s, the discovery of the concept of the Founder effect can be attributed to scientist Ernst Mayr[3] . Originally, Mayr called this phenomenon as the “peripatric speciation” or “founder-effect speciation“. In some New Guinea islands, Mayr observed that some populations of birds are very distinct from the main bird population. He hypothesized that this phenomenon could only occur by the isolation of a certain gene of the main population (resulting to bottleneck effect), genetic drift, and natural selection.

Throughout history, there have been several incidences where small groups of individuals move far from their home territories. By random chance alone, the new population develops different allele frequencies from that of the original population. Such isolation and evolution then leads to divergence between the two populations, with the founder population becoming a new species and being unable to interbreed with the former.

Examples of Founder Effect

In humans alone, Founder effect can be seen to govern the transmission of genes in some populations. In fact, there have been several examples of Founder effect in human populations across the globe, with most cases being genetic disorders.

The following are some of them:

1. Huntington’s Disease

Woody Guthrie (with Huntington's Disease)
Woody Guthrie was a famous singer-songwriter from 1930’s (diagnosed with Genetic disorder: Huntington’s Disease. Image: Wikimedia)
Huntington’s disease[4] is a heritable progressive neurological disorder characterized by uncontrolled motor function, and loss of intellectual capacity. Individuals who inherit the defective dominant allele tend to lose their control over their brains, and not long after, will die.

  • To date, it is present that this disease affects 0. 005 % (about 1 out of 20,000) people of European ancestry. Interestingly, fishing villages located near Lake Macaraibo (Venezuela) have the highest prevalence of this disease in the world.
  • The origin of this disease[5] can be traced back from a woman (in the 1700s) who carried the allele for Huntington’s disease and bore 10 children. These children and their children interbred and eventually created the lineage in that area.
  • On the other hand, this disorder is least observed in some populations like the Chinese, Japanese, and African ancestry.

2. Tay-Sach’s Disease

Another genetic condition governed by the principles of Founder effect is Tay-Sachs disease[6] . This disorder is known to destroy the nerve cells of the central nervous system and is usually fatal during early childhood.

  • The symptoms[7] of the disease include intellectual disability, seizures, paralysis and a cherry red spot eye abnormality. Because of these symptoms, the Cajuns (from Louisiana) also call this disease “Lazy Baby” syndrome.
  • Generally, about 0.4 % (or 1 out of 250 people) of the general population is a carrier of the allele for Tay-Sach’s disease. However, this disease has higher frequencies (about 3.7% or 1 out of 27 people) in the populations of the Ashkenazi, the French Canadians, and the Cajuns.
  • In the 17th century, the Cajuns, who originated from the French Canadians, migrated to Louisiana and carried the allele for Tay-Sach’s disease in their gene pool. Since then, the Cajuns remained isolated to the point that people married even their close relatives.

3. Ellis-Van-Creveld Syndrome

Ellis-van-Creveld Syndrome is another heritable condition that affects bone growth, resulting to dwarfism (overall short stature) and polydactyly (presence of extra fingers or toes). Affected individuals may also have life-threatening heart ailments.

  • This disorder is very rare in the general population[8] (1 out of 200 000 people) but is very much common in the Old Order Amish descent of Pennsylvania and Western Australia.
  • In the late 1930s, scientists Richard Ellis and Simon van Creveld first described the syndrome. Ten years later, the syndrome was formally described and was finally named after them.

Regardless of whether good or bad, Founder effect has indeed drastically affected populations. In addition to that, it has somehow contributed to the speciation and evolution of species present today.

Hence, a greater understanding of the evolutionary histories of the disorders in some populations will lead to the reduction of their further spreading in the long term; hence allowing people to be informed of their reproductive choices. To date, most genetic disorders that were results of Founder effect still don’t have any cures yet.

And despite of the advancement in technology, scientists are still puzzled by the questions:

How do these genes, which only exist in colonized environments, be common in some environments with such strong selection forces? Shouldn’t natural selection remove them already?

Cite this article as: "Mechanisms Of Evolutionary Change: The Founder Effect," in Bio Explorer, May 15, 2017, https://www.bioexplorer.net/founder-effect.html/.

References

  • [1] – “Mechanisms of Evolutionary Change.” Nectunt. Accessed May 14, 2017. Link.
  • [2]“Bottlenecks and Founder Effects”. Accessed May 14, 2017. Link.
  • [3]“On the Importance of Being Ernst Mayr”. Accessed May 14, 2017. Link.
  • [4]“Huntington disease – Genetics Home Reference”. Accessed May 14, 2017. Link.
  • [5]“Huntington’s Chorea: Evolution and Genetic Disease”. Accessed May 14, 2017. Link.
  • [6]“Google Docs – create and edit documents online, for free.”. Accessed May 14, 2017. Link.
  • [7]“Tay-Sachs disease – Genetics Home Reference”. Accessed May 14, 2017. Link.
  • [8]“Ellis-van Creveld syndrome – Genetics Home Reference”. Accessed May 14, 2017. Link.
Mechanisms Of Evolutionary Change: The Founder Effect
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