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Abstract
A general imbalance in the proportion of disembarked males and females in the Americas has been documented during the Trans-Atlantic Slave Trade and the Colonial Era and, although less prominent, more recently. This imbalance may have left a signature on the genomes of modern-day populations characterised by high levels of admixture. The analysis of the uniparental systems and the evaluation of continental proportion ratio of autosomal and X chromosomes revealed a general sex imbalance towards males for European and females for African and Indigenous American ancestries. However, the consistency and degree of this imbalance are variable, suggesting that other factors, such as cultural and social practices, may have played a role in shaping it. Moreover, very few investigations have evaluated the sex imbalance using haplotype data, containing more critical information than genotypes. Here, we analysed genome-wide data for more than 5000 admixed American individuals to assess the presence, direction and magnitude of sex-biased admixture in the Americas. For this purpose, we applied two haplotype-based approaches, ELAI and NNLS, and we compared them with a genotype-based method, ADMIXTURE. In doing so, besides a general agreement between methods, we unravelled that the post-colonial admixture dynamics show higher complexity than previously described.
Highlights
Present-day populations living in the Americas trace their ancestry to Indigenous groups, together with influxes from multiple sources from Africa and Eurasia, due to a complex history of admixture following the Atlantic Slave Trade, the Colonial Era, and more recent migration phenomena [1]
In Ongaro et al 2019 [6], where we applied ADMIXTURE [22], we found that the distribution of autosomal vs. X chromosomes for the European ancestry is significantly higher in all comparisons, suggesting a more significant contribution of European males than females in the gene pool of American populations
We applied two haplotype-based methods (ELAI and non-negative least square (NNLS)) on a dataset composed of 5242 individuals for the X chromosome and the autosomes (Supplementary Table S1)
Summary
Present-day populations living in the Americas trace their ancestry to Indigenous groups, together with influxes from multiple sources from Africa and Eurasia, due to a complex history of admixture following the Atlantic Slave Trade, the Colonial Era, and more recent migration phenomena [1]. Early surveys based on uniparental markers suggested the existence of a sex-biased admixture history, with a higher degree of American and African mitochondrial DNA when compared to their Y-chromosome counterpart [11,12,13,14,15]. This evidence is possibly the result of more European males mating with American and African females.
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