Population structure and immigration; a study of the Valserine valley (French Jura) from the 17th century until the present.

The establishment of the genealogies and biographies of inhabitants of selected villages from the Haut-Jura from the 17th century up to the present day has enabled us to demonstrate the major role of immigration on the genetic structure of a population. The evaluation of the effective descendance of native versus immigrant couples shows the imbalance of demographic contribution in favour of the first category. Immigrant couples account for 26% of all couples with at least one offspring in the valley, but account for 7.2% of all couples with an effective descendance. In our opinion, this effective immigration reflects in a much better way the measurement of immigration impact on population genetic parameters, especially the genetic 'opening' of the population due to immigration. This measurement of the effective descendance divides the population into two major groups: a core of stable lineage characterized by 70% of couples with an effective descendance, 'surrounded' by an unstable group from which only 30% of couples have an effective descendence in the population. Furthermore, from any given point in time this difference between the two groups can be observed among their descendants during the following generations. The existence of such a core can be explained by the social history of the valley, and shows that any specific unfavorable genetic fostered by the core can be locked within the population and transmitted throughout generations.