In biology,
is a random occurrence that leads to a change in frequency of a certain allele within a species. The
is a type of genetic drift in which the number of individuals has been reduced due to a natural disaster, leading to a decrease in frequency of certain alleles. Another form of genetic drift is the
, in which a number of individuals separate from their population to form a new colony and in turn change the frequency of certain alleles. Genetic drift has a more significant effect on
​​​​​​​ populations of species.