The correlation between ancestry and color in two cities of Northeast Brazil with contrasting ethnic compositions

Abstract

The degree of admixture in Brazil between historically isolated populations is complex and geographically variable. Studies differ as to what the genetic and phenotypic consequences of this mixing have been. In Northeastern Brazil, we enrolled 522 residents of Salvador and 620 of Fortaleza whose distributions of self-declared color were comparable to those in the national census. Using the program Structure and principal components analysis there was a clear correlation between biogeographic ancestry and categories of skin color. This correlation with African ancestry was stronger in Salvador (r=0.585; P<0.001) than in Fortaleza (r=0.236; P<0.001). In Fortaleza, although self-declared blacks had a greater proportion of European ancestry, they had more African ancestry than the other categories. When the populations were analyzed without pseudoancestors, as in some studies, the relationship of 'race' to genetic ancestry tended to diffuse or disappear. The inclusion of different African populations also influenced ancestry estimates. The percentage of unlinked ancestry informative markers in linkage disequilibrium, a measure of population structure, was 3-5 times higher in both Brazilian populations than expected by chance. We propose that certain methods, ascertainment bias and population history of the specific populations surveyed can result in failure to demonstrate a correlation between skin color and genetic ancestry. Population structure in Brazil has important implications for genetic studies, but genetic ancestry is irrelevant for how individuals are treated in society, their health, their income or their inclusion. These track more closely with perceived skin color than genetic ancestry.

Genomic ancestry and ethnoracial self-classification based on 5,871 community-dwelling Brazilians (The Epigen Initiative)

“…This was to such a degree that it has been questioned whether – and how – ethnoracial classification in Brazil correlates with genomic ancestry. Previous genome studies based on up to a hundred informative markers showed conflicting results on this correlation345678.…”

Epidemiology and treatment of psoriasis: a Brazilian perspective

“…Population studies evaluating the prevalence and distribution of this disease among races have not yet been performed. Despite the absence of psoriasis among natives of the Andean region of South America, 45 Brazil has a highly miscegenated population; as a result, a dissociation between skin color and genomic ancestry 46 makes it unlikely that identical results will be obtained in Amerindian Brazilians. Because Brazilian government protocol contradicts the national consensus regarding the treatment of psoriasis, studies of cost-effectiveness and additional investments in phototherapy and systemic drug availability are urgent.…”

Summaries of plenary, symposia, and oral sessions at the XXII World Congress of Psychiatric Genetics, Copenhagen, Denmark, 12–16 October 2014

“…Brazil is noteworthy for a huge population expansion since the start of the 19th century and for having been the destination of 40% of the Trans-Atlantic slave trade. This makes it an admixture melting pot, with patterns that reflect the original colonization of the territory (Salzano and Sans, 2014; Magalhaes Da Silva et al, 2015). Although the first genetic studies in Brazil started in the 1980s, interest in genetics increased after the publication of the first ‘Brazilian Genome Project’, the plant pathogen Xyllela fastidiosa (Simpson et al, 2000).…”