9.4 Genetic drift

Random genetic drift/ Sewall Wright effect

The occurrence of characteristics in a population as a result of chance rather than natural selection. It occurs only in small populations.

Founder effect

Is an extreme example of genetic drift. This effect occurs when a small group moves away from its homeland to a totally new area and establishes a population, which later expands.

New groups formed by the founder effect because of it small size can have… 

• A different allele frequency from the original population

• decreased genetic variation

Bottleneck effect

Is an extreme example of genetic drift. In this situation an event such as a natural disaster severely reduces the size of the population. The allele frequency after the disaster, by chance be different from before the event. The chance of survival is by chance and not due to a specific trait.