Deciphering the genetic structure of the Quebec founder population using genealogies

Using genealogy to study the demographic history of a population makes it possible to overcome the models and assumptions often used in population genetics. The Quebec founder population is one of the few populations in the World having access to the complete genealogy of the last 400 years. The goal of this paper is to follow the evolution of the Quebec population structure generation per generation from the beginning of European colonization until the present day. To do so, we calculated the kinship coefficients of all ancestors’ pairs in the ascending genealogy of 665 individuals from eight regional and ethnocultural groups per 25-year period. We show that the Quebec population structure appeared in the St. Lawrence valley as early as 1750. At that time, the ancestors of two groups, the Sagueneans and the Acadians from the Gaspé Peninsula, experienced a marked increase in kinship and inbreeding levels which have shaped the contemporary population structure. Interestingly, this structure arose before the colonization of the Saguenay region and at the very beginning of the Gaspé Peninsula settlement. The resulting regional founder effects in these two groups, but also in the other regional groups, led to differences in the present-day identity-by-descent sharing and are directly linked to the number of most recent common ancestors and their genetic contribution to the studied subjects.