Abstract
Based on pre-DNA racial/color methodology, clinical and pharmacological trials have traditionally considered the different geographical regions of Brazil as being very heterogeneous. We wished to ascertain how such diversity of regional color categories correlated with ancestry. Using a panel of 40 validated ancestry-informative insertion-deletion DNA polymorphisms we estimated individually the European, African and Amerindian ancestry components of 934 self-categorized White, Brown or Black Brazilians from the four most populous regions of the Country. We unraveled great ancestral diversity between and within the different regions. Especially, color categories in the northern part of Brazil diverged significantly in their ancestry proportions from their counterparts in the southern part of the Country, indicating that diverse regional semantics were being used in the self-classification as White, Brown or Black. To circumvent these regional subjective differences in color perception, we estimated the general ancestry proportions of each of the four regions in a form independent of color considerations. For that, we multiplied the proportions of a given ancestry in a given color category by the official census information about the proportion of that color category in the specific region, to arrive at a “total ancestry” estimate. Once such a calculation was performed, there emerged a much higher level of uniformity than previously expected. In all regions studied, the European ancestry was predominant, with proportions ranging from 60.6% in the Northeast to 77.7% in the South. We propose that the immigration of six million Europeans to Brazil in the 19th and 20th centuries - a phenomenon described and intended as the “whitening of Brazil” - is in large part responsible for dissipating previous ancestry dissimilarities that reflected region-specific population histories. These findings, of both clinical and sociological importance for Brazil, should also be relevant to other countries with ancestrally admixed populations.
Highlights
Continental populations of the world vary considerably in their predisposition to diseases and in the allele frequencies of important pharmacogenetic loci, probably as a result of genetic drift, and because of adaptation to local selective factors such as climate and available nutrients
The trihybrid ancestry of Brazilians from different regions We here present results of the molecular estimation of the European, African, and Amerindian ancestry in 934 individuals belonging to different color categories and originated from four regions of Brazil (Figure 1)
In a previous publication [9], with different samples, a weak relationship had already perceived between color and geographic genomic ancestry in Brazilians at an individual level, as we observed in the present study
Summary
Continental populations of the world vary considerably in their predisposition to diseases and in the allele frequencies of important pharmacogenetic loci, probably as a result of genetic drift, and because of adaptation to local selective factors such as climate and available nutrients. The Brazilian population was formed by extensive admixture from three different ancestral roots: Amerindians, Europeans and Africans. This resulted in a great variability of skin pigmentation, with no discontinuities between Black and White. In a single small fishing village in Brazil, Harris and Kotak [1] identified dozens of designations for varied shades of skin pigmentation
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