Random genetic drift in a population probably results from:

Genetic drift (Sewall Wright effect) is the random change in the frequency of alleles in a population over successive generations in the gametes. Each new generation differs from its parental generation with regard to allele frequencies simply because of random variation in the distribution of gametes. This process is more rapid in smaller populations, or when the alleles concerned confer no apparent benefit compared to their counterparts. Related Theory A founder effect occurs when a new colony is started by a few members of the original population. This small population size means that the colony may have reduced genetic variation from the original population and a non-random sample of the genes in the original population.