Genetic drift can obscure population history: problem and solution.

Genetic distances between populations can be derived from a wide variety of data and have been applied to studies of population structure and history ranging from local groups to an entire species. Genetic distances measure the effects of both population history (historical relations and migration) and population structure (migration and drift). Frequently, we are interested in assessing population history, and any impact of differential genetic drift is likely to confound our interpretations. I show here that when population sizes are different, differential genetic drift can obscure the underlying pattern of population history. Previous genetic distance studies have failed to take genetic drift into account when reconstructing population history. A simple method is presented here that takes into account differences in population size and differential drift. This method is illustrated using allele frequencies from Jewish and non-Jewish populations in six Old World regions. The scaled distances provide a clearer picture of population history than the traditional unscaled distances.