Founder Effect

Because the founder population is small, genetic drift can play an important role in determining the genetic makeup of subsequent generations, and allele frequencies may fluctuate. For example, consider an extreme situation where a new population is founded by just two individuals, a male and a female, perhaps because they are stranded on an island. Assume that the The Hutterite colony, to which these children belong, is a founder population with a high prevalence of asthma. mother is heterozygous for a particular allele (Aa), while the father is homozygous (AA). If the couple has two children, there is a 25 percent chance that the mother will pass the A allele to both children.

If neither child inherits the allele, the a allele is effectively lost from the population. Even as they grow, many founder populations remain relatively genetically isolated, with little immigration into the population. Examples include founder populations that have remained isolated due to geographical location, such as Finland and Iceland, or due to religious customs, such as Amish and Hasidic Jewish groups.

Founder populations may have increased prevalence of certain genetic traits, including genetic disease. Disease alleles that happen to be present in the founders may be passed on to offspring, and, since the population is small, there may be a higher prevalence of the disease than in other, larger populations. Isolated founder populations, with little marriage outside of the populations, are especially likely to have a higher prevalence of recessive disorders, since parents are likely to share many genes, and there is an increased chance of inheriting two copies of a particular disease gene. Examples of rare genetic diseases that are prevalent in founder populations are Tay-Sachs disease in Ashkenazic Jewish populations and asthma in the Hutterian population.