The terms "founder populations" and "isolated populations" are used at least partially as interchangeable synonyms.

Compared with mixed populations with large genetic and environmental diversity, population islands, isolated by linguistic-cultural (e.g. Saami, Basque), religious (e.g. Amish, Mennonites, Hutterers) or geographic (islands, mountain valleys) factors, present the genetic researcher with a number of advantages.

© Udo Bernhart / NG-D

Such population islands are particularly well suited to the analysis  of the complex interaction between genes and the environment because of their relative genetic homogeneity and similar environmental conditions.

© Udo Bernhart / NG-D

Analyses of chromosomal and mitochondrial DNA have demonstrated that such population islands exhibit significantly less genetic diversity than mankind as a whole because their populations descend from just a few founding parents.  So-called "bottleneck" events alternate with periods of rapid population growth.

Bottleneck events can be caused by famine, epidemic diseases or natural disasters, and are characterised by a dramatic decrease in population, followed by renewed population growth. The settlement of a microisolated population by a limited number of parents has a similar effect.  The genetic diversity of such a population is small and no longer corresponds to the pattern of allele (gene pair) distribution in a normal population.

Only a few isolated populations, like Iceland, Finland, Sardinia or South Tyrol, possess genealogical records dating back several centuries.  Using this data, information about the number of founders and the biodemographic development of the population can be derived. 

South Tyrol, with its German- and Ladin-speaking groups, has two distinct isolated populations that can be distinguished by their relative ages, like Finland (with its Saami and Finn peoples). Such isolates are characterised by either very old or recent population-specific mutations, accordingly. In younger isolated populations (like the german-speaking microisolated groups in South Tyrol) with little migration, genetic diversity is also reduced by genetic drift, but not as drastically as in very old isolated groups like the Ladins, who are of Palaeolithic origin. This difference between the two isolated groups allows different approaches in the genetic studies.

Photos by Udo Bernhart courtesy of National Geographic Deutschland