FIG. 3.

How genetic isolation leads to loss of shared polymorphisms in descendent populations. In the absence of selection to maintain polymorphisms, the fate of all polymorphic loci is fixation through genetic drift. Beginning with two genetically isolated populations that share the polymorphism of the ancestral population, first one and then the other population becomes fixed for one allele. In this case, the two descendent populations have become fixed for alternate alleles, making this locus useful for determining the population of an unknown individual.