Genetic Threads: Mapping the French Canadian Tapestry Through Space and Time

News and Views by: Gabe Jones (gajones@davidson.edu)

Primary Article: Anderson-Trocméet al. 2023

Analyzing the nuanced genetic history of French Canadians, this research, employing an extensive spatial pedigree, reveals how historical events, geography, and migration have shaped their unique genetic landscape. By highlighting distinctive founder events this study forms the crucial link between family pedigrees, natural topography , and theoretical models that may serve as a novel way to investigate other population genetics.

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6 million French Canadians trace their ancestry back to approximately 8500 permanent French settlers. The legacy of these settlers who colonized Nouvelle France between 1608 and 1759 unfolds through well-documented parish manuscripts, internal migrations, and four centuries of relative isolation (Scriver 2001). This isolation, encompassing geographical and societal aspects, played a crucial role in shaping the population structures still seen today. Their distinctive genetic background has led to a higher prevalence of rare genetic diseases in the region, prompting comprehensive studies to identify causal genes and variants associated with these conditions (Bchetnia et al. 2020). Thus, delving into the rich genetic history of French Canadians, the study navigates the intricate tapestry of their ancestry, addressing the challenge of coordinating continuous genetic variation into discrete “evolutionarily significant units” (Anderson-Trocméet al. 2023). In their efforts in accomplishing this, their collected mapped data reveals a compelling narrative of historical migrations, geographic influences, and the complex interplay between human movement and genetic diversity.

To accomplish this the researchers used a vast collection of Catholic parish records from Quebec. These extensive records are public access and date back to 1621 hosting the original documentation of each Catholic wedding, baptism, and death. With this resource they created a large-scale family tree, called a spatial pedigree, that includes information on 20,451 French Canadian individuals. Imagine it like a detailed map of family connections spanning over 400 years. To understand the genetic makeup, they employed two visual tools, PCA and UMAP, which are like special lenses to see patterns in the data. Picture it as a way to view the unique genetic landscape, highlighting the relationships between people and their shared ancestry. These tools were then used in tandem with the msprime software to generate simulations of whole genomes for 1.4 million present-day individuals. Of which the correlation to the selected 4882 individuals genotyped for this study was impeccably similar. This extensive simulated dataset, accompanied by the spatiotemporal metadata, is made freely available for further genetic modeling and research.

The conglomerate of genetic data unveils distinct regional sagas of founder events across Quebec, underscoring Quebec City as a central hub for these historical narratives (Figure 1). In the Saguenay–Lac-Saint-Jean (SLSJ) region, Baie-Saint-Paul emerges as a pivotal site for a dominant early founder event, shaped by the geological after effects of erosion from Charlevoix’s impact crater. This geological feature, crafting a fertile terrain amid a rugged mountainous region, triggered demographic pressures and swift expansion along the Saguenay River which established profound ancestral ties over a large area of land predating the formal SLSJ colonization, which occurred during of the 19th century (McComber 2006). The Beauce region showcases Saint-Joseph-De-Beauce as a key player in a founder event, embodying a hub-and-spoke migration pattern along the Chaudière River (think of many directional migrations out of this nexus region). Likewise, Bas-Saint-Laurent unfolds a mosaic of founder events, with Rivière-Ouelle at the forefront and minor events dotting extensive shorelines, serving as regional hubs for subsequent migrations inland. This pattern coincides with the importance of rivers in early settlement strategies, transportation, and commercial activity.

Quantifying the contributions of those who partook in the founding events reveals the isolation in which these events took place. The authors highlight the significant contributions of “superfounders” (referring to the earliest settlers that migrated) to present-day populations. The top 10 superfounders in each region played pivotal roles, contributing 37%, 14%, and 12% of the genetic similarity in SLSJ, Beauce and , Bas-Saint-Laurent respectively. Of note, while each region exhibits its oldest and strongest founder event near Quebec City, no two regions share the same superfounders. Analysis of their ancestral genetic mapping reveal that 35-50% of kinship in Bas-Saint-Laurent and Beauce can be attributed to a shared founder event, contrasting with SLSJ, where only 5% is shared due to the region-specific founder events in Charlevoix Moreover, Abitibi-Témiscamingue, despite a similar frontier expansion process to SLSJ, showed limited evidence of shared patterns between its sampled villages. Whereas sampled villages in SLSJ exhibit 70% genetic overlap, despite being over 100 km apart, underscoring the unique spatially defined founder events and the intricate patterns of human evolutionary dynamics over time.

To bring it all back, this genetic cartography unravels the unique historical tales that have intricately woven the diverse genetic fabric characterizing different Quebec regions. The study serves as a monument in how we can simulate past migrations in an immensely accurate manner to piece together why certain populations are more genetically similar over larger land masses than others that may be contained in much smaller geographical regions. Thinking more broadly, this series of events explains the increase in what would typically be called a “rare” diseases among these populations that trace their lineage back to Quebec City. While ethical or societal questions may be asked in regard to claiming that someone is more or less predisposed to health discrepancies due their ancestors, the data argues that is not an opinion, but a fact. that these people may experience conditions considered “rare” on a global scale, in a more frequent occurrence. Moving forward, replicating a study like this may prove difficult as it was the extensive records of the church that catalyzed this project, however many cultures have records that may date back even before the 15th century and they deserve to have their ancestral immigration patterns known someday as well. Maybe it will reveal the reoccurrence of a rare allele that was adopted to combat an ancient illness, or maybe it will just make someone’s 23&ME results just a little bit more accurate.

References:
1) Anderson-Trocmé L, Nelson D, Zabad S, Diaz-Papkovich A, Kryukov I, Baya N, Touvier M, Jeffery B, Dina C, Vézina H, Kelleher J, Gravel S. On the genes, genealogies, and geographies of Quebec. Science 2023; 380: 849–855. [DOI: 10.1126/science.add5300]

2) Maria Laplante McComber Saguenay-Lac-Saint-Jean, Que | The Canadian Encyclopedia. Available from: https://www.thecanadianencyclopedia.ca/en/article/saguenay-lac-saint-jean-que-emc

3) Mbarka Bchetnia, Luigi Bouchard, Jean Mathieu, Philippe M. Campeau, Charles Morin, Diane Brisson, Anne-Marie Laberge, Hélène Vézina, Daniel Gaudet, Catherine Laprise. “Genetic burden linked to founder effects in Saguenay–Lac-Saint-Jean illustrates the importance of genetic screening test availability.https://jmg.bmj.com/content/58/10/653

4) Scriver CR. Human Genetics: Lessons from Quebec Populations. Annual Review of Genomics and Human Genetics 2001; 2: 69–101. [PMID: 11701644 DOI: 10.1146/annurev.genom.2.1.69]

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