What is Genetic drift?
'''Genetic drift''' is a [[random]] effect on biological [[population]]s. Its effect is to remove [[genetic]] [[variation (biology)|variation]] from a population of living [[organism]]s.<ref name=pop>Gillespie, John H. 2004. ''Population genetics: a concise guide''. 2nd ed, Johns Hopkins University Press, Baltimore. Chapter 2 and 4.3 {{ISBN|0801880092}}</ref> In natural populations there are a number of forces acting. There are forces which add [[heritable]] variation to the population, such as [[mutation]] and [[recombination]]. There are also factors which remove variation from the population, and drift is one of these. == Overview == In a species, or an interbreeding population, there is usually a great deal of genetic variation. This genetic variation is in the form of different [[allele]]s at many [[Allele|loci]] (gene positions) on the [[chromosome]]s. Changes in [[allele frequency]] are mainly caused by [[natural selection]], that is, by differential survival, and contribution to the next generation. But as populations get smaller, there is a tendency for each generation to become more [[homozygous]], with less variety of alleles. This is an effect similar to [[inbreeding]]: it leads to genetic uniformity. Genetic drift is the name given to this loss of variation. It can affect evolution in surprisingly big ways, but ''only when populations are quite small''. What 'small' means would depend on the organism. 50 individuals is small, 5000 is not, 500 is maybe. The basic mechanism of drift is that genetic variety is reduced by chance, making the individuals more similar to each other, and hence more vulnerable. Genetic drift reduces genetic variation in populations, potentially reducing a population’s ability to survive new selective pressures. Genetic drift acts faster and has more drastic results in smaller populations.<ref>Klug W.S. ''et al'' 2012. ''Concepts of genetics''. Pearson, p710. {{ISBN|0-321-79578-4}}</ref> The effects of gentic drift on small populations can vary due to evoultionary chan