Genetic Drift

1. Genetic Drift Genetic Drift Genetic Bottleneck The Founder Effect

2. Genetic Drift - What is it? 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

3. Genetic Bottlenecks 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. Many events can cause Genetic Bottlenecks such as: Droughts Human Destruction Earthquakes 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

4. Genetic Bottlenecks • 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.

5. The Founder Effect 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 New Population – less genetic variation Initial Population

6. 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.

7. Summary 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