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PgmNr 2349: The genetic consequences in the Americas of the transatlantic slave trade.

S. Micheletti 1; K. Bryc 1; S. Ancona Esselmann 1; W. Freyman 1; M. Moreno 1; A. Shastri 1; S. Beleza 2; J. Mountain 1

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1) 23andMe, 899 W Evelyn Ave, Mountain View, CA 94041, US; 2) University of Leicester, University Rd, Leicester LE1 7RH, UK

The transatlantic slave trade marks the largest forced migration event in history, involving the deportation of an estimated 12.5 million Africans. Occurring between the 15th and 19th centuries, the slave trade involved nearly every country with an Atlantic coastline and has continued to impact the world more than a century after its abolition. Even though shipping records document the number of enslaved people disembarking across the Americas, there have been very few broad-scale genetic studies of populations across all of the Americas with ancestral ties to the transatlantic slave trade. In this study, we utilized high-density genotype data from over 25,000 23andMe research participants with western African ancestry to determine how the transatlantic slave trade has shaped populations across twenty-eight regions within the United States, Latin America, and the Caribbean. Using 23andMe's Ancestry Composition algorithm, which detects ancestry from multiple subregions of western Africa, we show that individuals with African ancestry in the Americas tend to have connections with multiple historical slave trading regions in western Africa. However, the most frequently inferred western African ancestries differ across the Americas. For instance, individuals in the United States and Caribbean tend to have connections with all historical slave trading regions in western Africa, while individuals from Latin America tend to have ancestry primarily from either west central Africa or Senegambia. To estimate the temporal connection between populations in the Americas and West Africa, we identified DNA identical by descent (IBD) between all twenty-eight disembarkment regions and seven historical embarkment regions in western and southwestern Africa. We used the distribution of IBD segment lengths to determine the probability that shared IBD between regions were inherited from a common ancestor who embarked from western Africa during the 400-year period of the transatlantic slave trade. Results suggest that genetic estimates of time to most recent common ancestor are generally concordant with documented embarkment dates from western Africa. Overall, this study provides an unprecedented investigation of the transatlantic slave trade, establishing genetic links between populations in the Americas to populations in western Africa, which has implications for individuals’ understanding of their African roots.