An extreme case of gene drift is the so-called founder's principle: a new population is “founded” by one or a few individuals, either because the ancestral population has declined drastically, or because a small number of individuals in one population have migrated to another region. , where it gave rise to a new population.
Under these conditions, the individuals who started the new population, being few, usually do not constitute a representative sample of the original population. There are cases when a single pregnant female founds a new population. This female will obviously not have a significant sample of the different types of alleles present in the original population.
Gene drift seems to have been a common phenomenon in the colonization of islands far from the continents, to which few individuals from continental populations can reach. On the islands, "founders" initiate populations whose gene frequencies are generally quite different from the original continental populations.
Example of the founding principle in man
An example of the founding principle in the human species was found in religious communities of German origin that settled in the United States. Due to their customs and religion, the members of these communities, called Dunker, remained isolated from the American population.
Frequency analysis of some genes in the Dunker community members showed significant differences in both the US population and the German population. Gene frequency differences in the Dunker population cannot be attributed to selective environmental factors, as these would also have acted on the North American population.
The most plausible explanation is that the North American Dunkers from Germany were not a representative sample of the German population regarding the frequencies of the genes analyzed. In the United States, as they remained isolated, their gene frequencies remained differentiated from the North American population.