Genetic Drift

Genetic Drift Genetic Bottleneck The Founder Effect

Genetic Drift Genetic drift is the change of

allele frequency (which is the relative frequency of alleles) in populations due to random chance

The changes in allele frequency are due to chance and cause random shifting in genetic make ups from one generation to another

The event of genetic drift has a greater effect on smaller populations as they are more susceptible to dramatic changes in alleles and even extinction of the alleles may occur

- What is it?

Genetic Drift

Genetic Bottleneckso Genetic Bottlenecks are

dramatic decreases in the number of organisms in large populations, and due to genetic drift, the allele frequencies in a population changes.

o Many events can cause Genetic Bottlenecks such as:

Droughts Human Destruction Earthquakes

o The Northern elephant seals are an example of organisms that were impacted from Genetic Bottlenecks due to human inflictions – they have much less genetic variations between one another as their population size decreased by being hunted

If surviving organisms are able to recover from the disaster, they will have different allele frequencies than the initial population – if the original population was smaller, the variations in genetic pools would reduce faster and some may even become extinct.

Genetic Bottlenecks

The Founder Effect The Founder Effect is a type of genetic drift that involves

small groups of organisms separating from a larger population and forming small, new colonies.

By chance, the allele frequencies in the small colony will differ to the ones in the original population – due to this, genetic variation is limited

The Founder Effect

Initial Population

New Population – less genetic variation

The Founder Effect

An example of the Founder Effect includes the finches on the Galapagos Islands. In the 1980’s, two scientists examined 238 finches of the original population (five were original founder birds) and 22 offspring. They discovered that the founder population had larger beaks and that this physical change occurred in such a short time span that it could not be considered a gradual change over time. These five original birds may have had high allele frequency for larger beaks.

In Summary: Genetic drift is the change of allele frequency due to random

chance and causes random shifting in genetic makeup from one generation to the other

Genetic drift has a more significant impact on smaller populations

Genetic Bottlenecks cause dramatic population decreases

The Founder Effect occurs when small groups separate by chance from large populations and form new colonies, causing the allele frequencies and genetic make up to be different

Summary