Update to Heyer's “One Founder/One Gene Hypothesis in a New Expanding Population” (1999)

Abstract

“One Founder/One Gene Hypothesis in a New Expanding Population” (Heyer 1999) was written as part of a more global project aiming to understand the processes by which several inherited recessive disorders reached a high frequency in the Saguenay region of Quebec. In the paper Heyer focused on a specific question: Was it likely that each disorder had been introduced in the ancestral population by a single founder? The Saguenay population was known for a long time for having been under strong founder effect (Bouchard and DeBraekeleer 1991). Indeed, approximately 5,000 founders who settled in “nouvelleFrance” in the 17th century are the ancestors of more than 300,000 individuals living nowadays in the Saguenay region (Heyer and Tremblay 1995). This is a tremendous population growth in only 10–12 generations. The question remained whether this strong increase alone could explain the high occurrence of severe genetic disorders in this population. Under the one founder/one gene hypothesis the increase in carrier frequency is from 1/5,000 to 1/25 (average present carrier frequency of most common recessive disorders). This represents a strong level of genetic drift, which is quite unlikely in a standard WrightFisher population (i.e., a population of neutral genes without specific demographic processes). Using ascending genealogies in the Human Biology paper, Heyer proved that such an increase was expected from the genealogical network of the population, confirming the one founder/one gene hypothesis. The next step of the work was to find the demographic process that could explain this tremendously strong increase of frequency of the disease alleles. Heyer showed the existence of a peculiar sociodemographic process: the inheritance of fertility through cultural transmission. This was evidenced by a positive correlation between the number of progeny of an individual and the number of progeny of his or her parents. Heyer computed this correlation using the demographic database built up by the Interdisciplinary Research Group on Demography and