Genetic drift

Genetic drift is defined as the change in allele frequency due to chance (VCAA 2013).Genetic drift events causes changes in the allele pool and its effects are more obvious in small populations. In VCE Biology we consider the founder effect and bottleneck effect as both examples of this process. 

Bottleneck effect

The bottleneck effect can be defined a severe reduction in genetic diversity due to a catastrophe that may change allele frequency (VCAA 2013). The variation in the gene pool at the end of the catastrophre is reduced in comparision to the variation that existed prior. This reduction continues to persist even if the survivors in the population proceed to reproduce, because some alleles have been removed from the population.


In the cheetah population their was a population crash a few thousand years ago and since then despite a gradual increase of the numbers of the cheetahs since after the crash there is little variation that exists since then in the current populations.

Founder effect

The founder effect can be described as the colonisation of an area by a limited number of individuals from a parent population that are not representative of the original population. The resultant population may be different on genetic and phenotypic basis.


The incidence of Polydactyl amount the Amish settlers population

See also