DNA tests probe the genomic ancestry of Brazilians |
DNA tests probe the genomic ancestry of Brazilians
Brazilian Journal of Medical and Biological Research
Volume 42, Number 10 (October 2009)
pages 870-876
DOI: 10.1590/S0100-879X2009005000026
S .D. J. Pena
GENE, Núcleo de Genética Médica, Belo Horizonte, MG, Brasil
Departamento de Bioquímica e Imunologia, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brasil
L. Bastos-Rodrigues
Departamento de Bioquímica e Imunologia, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brasil
J. R. Pimenta
GENE, Núcleo de Genética Médica, Belo Horizonte, MG, Brasil
S. P. Bydlowski
Laboratório de Genética e Hematologia Molecular (LIM-31), Faculdade de Medicina, Universidade de São Paulo, Hospital das Clínicas, São Paulo, SP, Brasil
We review studies from our laboratories using different molecular tools to characterize the ancestry of Brazilians in reference to their Amerindian, European and African roots. Initially we used uniparental DNA markers to investigate the contribution of distinct Y chromosome and mitochondrial DNA lineages to present-day populations. High levels of genetic admixture and strong directional mating between European males and Amerindian and African females were unraveled. We next analyzed different types of biparental autosomal polymorphisms. Especially useful was a set of 40 insertion-deletion polymorphisms (indels) that when studied worldwide proved exquisitely sensitive in discriminating between Amerindians, Europeans and Sub-Saharan Africans. When applied to the study of Brazilians these markers confirmed extensive genomic admixture, but also demonstrated a strong imprint of the massive European immigration wave in the 19th and 20th centuries. The high individual ancestral variability observed suggests that each Brazilian has a singular proportion of Amerindian, European and African ancestries in his mosaic genome. In Brazil, one cannot predict the color of persons from their genomic ancestry nor the opposite. Brazilians should be assessed on a personal basis, as 190 million human beings, and not as members of color groups.
Introduction
Brazilians are one of the most heterogeneous populations in the world, the result of five centuries of interethnic crosses between peoples from three continents: Amerindians, Europeans and Africans. Little is known about the number of indigenous people living in the area of what is now Brazil when the Portuguese arrived in 1500 (1), although a figure often cited is that of 2.5 million individuals. The Portuguese-Amerindian admixture started soon after the arrival of the first colonizers and later became commonplace, being even encouraged after 1755 as a strategy for population growth and colonial occupation of the country….
From the middle of the 16th century, Africans were brought to Brazil to work on sugarcane farms and, later, in the gold and diamond mines and on coffee plantations. Historical records suggest that between circa 1550 and 1850 (when the slave trade was abolished), around four million Africans arrived in Brazil (2)…
Uniparental genetic markers in Brazilians
…To learn about the maternal counterpart, we analyzed mtDNA, which revealed a different reality. Considering Brazil as a whole, 33, 39, and 28% of matrilineages were of Amerindian, European and African origin, respectively (9,12). As expected, the frequency of different regions reflected their genealogical histories: most matrilineal lineages in the Amazon region were of Amerindian origin, while African ancestrality was preponderant in the Northeast (44%) and European haplogroups were prevalent in the South (66%). These data have since been amply confirmed by numerous other studies. For instance, we recently analyzed the mtDNA haplogroup structure of 242 self-identified white individuals from São Paulo and ascertained 24% Amerindian, 22% African and 54% European matrilineal proportions (Dornelas HG, Bydlowski SP, Pena SDJ, unpublished data).
Next, for further confirmation, we studied mtDNA lineages in 120 black individuals from the city of São Paulo. The results, as expected, showed a mirror image of those previously found in white Brazilians: on the one hand, 85% of the lineages originated in Sub-Saharan Africa, 12% were from Amerindians and only 3% were from Europe; on the other, only 48% of the Y chromosome lineages originated from Sub-Saharan Africa (the vast majority belonging to haplogroups E3a7 and E3a*). Studies on black individuals from the cities of Rio de Janeiro and Porto Alegre produced very similar results.
Taken together, these numbers disclose a picture of very strong directional mating between European males and Amerindian and African females, which agrees perfectly with the known history of the peopling of Brazil since 1500. These studies also reveal that the genomes of most Brazilians are mosaic, having mtDNA and NRY of different phylogeographical origins.
Biparental genetic markers and ancestry in Brazilians
In Brazil, notwithstanding relatively large levels of genetic admixture and a myth of “racial democracy”, there exists widespread social prejudice that seems to be particularly connected to the physical appearance of an individual. Color (in Portuguese, cor) denotes the Brazilian equivalent of the English term race (raça) and is based on a complex phenotypic evaluation that takes into account, besides skin pigmentation, also hair type, nose shape and lip shape. The reason why the word color is preferred to race in Brazil is probably because it captures the continuous aspects of phenotypes. In contrast with the situation in the United States, there appears to be no racial descent rule operational in Brazil and it is possible for two siblings differing in color to belong to completely diverse racial categories.
Based on the criteria of self-classification of the 2000 census of the Instituto Brasileiro de Geografia e Estatística (IBGE), the Brazilian population was then composed of 53.4% Whites, 6.1% Blacks and 38.9% Brown (“pardos” in Portuguese). How do these numbers correlate with genomic ancestry?..
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Tags: Brazilian Journal of Medical and Biological Research, J. R. Pimenta, L. Bastos-Rodrigues, S .D. J. Pena, S. P. Bydlowski