Genetic drift refers to the alteration in the frequencies of alleles in the gene pool of a finite population due to chance events. It takes place in one or over a few generations. If the change in the allele frequencies is very drastic, then new species are formed. If the population is finite or limited, a random selection of alleles occurs and in such a scenario, the frequencies of alleles in a sample may not be the same as the frequencies of alleles in the total population. This is known as sampling error.