What Is the Founder Effect? — Definition & Examples

How Are Genetic Drift and the Founder Effect Related?

The founder effect is a type of genetic drift. Genetic drift is defined as a random change in allele frequency. Recall that alleles are different forms of a specific gene located in the same place on a chromosome. Eye color is an inherited trait that is influenced by several alleles.

So, genetic drift happens when some random individuals in a population that have a specific allele somehow leave more descendants behind than the other members. After a while, the alleles passed down by that population might be more or less common than they initially were.

So, What's the Founder Effect?

The founder effect happens when part of a larger population moves to a new location. They have left their original population and become their own unique population. These individuals might carry alleles that don't really represent the alleles of the parent population.

Here's an Example

Picture two red-haired people from a city of mostly brunettes. Imagine these red-heads build a new town with a few other people. Eventually, they have children. The red-heads would pass down the allele for red hair to their children.

After a few generations, there are now about 200 individuals in the population. Most of the town's population might end up having red hair. This new community is completely different from the city those few original people moved from. Thus, genetic drift has occurred as a result of the founder effect.

$$\color{#8925AE}{\text{Vocabulary Review:}}$$

$\color{#8925AE}{\text{Genetic Drift}}$ : A random change of allele frequency in a gene pool

$\color{#8925AE}{\text{Allele Frequency}}$ : How often a certain allele is expressed by a population

$\color{#8925AE}{\text{Founder Effect}}$ : Happens when a part of a population moves to a new location. These individuals might carry alleles that don't really represent the alleles of the original population

$\color{#8925AE}{\text{Bottleneck Effect}}$ : A population bottleneck happens when the population size is dramatically reduced due to natural disasters

The Founder Effect

Genetic drift is another mechanism of evolution. It is most common among smaller populations.

One form of genetic drift is the founder effect. It occurs when a small number of individuals populates a new area for the first time, so it usually occurs on islands and other geographically isolated places.

Low Genetic Variation

Populations that start out this way generally have limited genetic variation since they came from such a small pool of allele combinations. They usually have unique genotypes and phenotypes not seen in the original population. This can also lead to speciation because this new group is isolated from the original population.

Unless other organisms migrate to the area and mingle, genetic mutation is the only way new alleles can enter the population. As a result, populations of founder species are especially sensitive to habitat and environmental changes, and genetic disease.

Examples of Genetic Drift

Afrikaner Dutch Population

We can see some interesting examples of this effect in human populations. A small number of colonists made up the Afrikaner population of Dutch settlers. The descendants of these colonists have a very high level of the gene which causes Huntington's disease.

Although the general Dutch population does not exhibit a high level of Huntington's disease, the small group of original settlers in South Africa likely carried this gene at a higher frequency by random chance. The founder effect can still be seen generations later. It is a perfect example of how powerful genetic drift as a whole can be.

Old Order Amish of Pennsylvania

One more example is close to home for us. You can observe it in the Amish of Eastern Pennsylvania in Lancaster County. This population started with a small group of German settlers who made their home in Lancaster. The Amish marry within their own community, so new genetic variations don't enter the population often. One condition that exists in their gene pool is Ellis-van Creveld syndrome. This is a rare form of dwarfism that causes things like polydactyly (extra fingers or toes) and heart conditions. It is very common in this particular Amish community, but not in other places throughout Pennsylvania.

(Video) Genetic Drift

by The Amoeba Sisters

Genetic drift is another mechanism of evolution. It is most common among smaller populations. In this video, the Amoeba Sisters discuss genetic drift.