Genetic drift operates in:

Genetic drift is changes in allele frequencies of a gene pool due to chance or random events. This can occur in large or small populations. It causes gene pools of two isolated populations to become dissimilar as some alleles are lost and other are fixed. However, It acts faster and has more drastic results in smaller populations. This effect is particularly important in rare and endangered species. Genetic drift can contribute to speciation. For example, a small isolated population may diverge from the larger population through genetic drift.