Race and Ethnicity in Brazil - Genetic Studies - Admixture

Admixture

Genetic research on ancestry of Brazilians of different races has extensively shown that, regardless of skin colour, Brazilians generally have European, African, and Amerindian ancestors.

According to a genetic study about Brazilians, on the paternal side, 98% of the White Brazilian Y Chromosome comes from a European male ancestor, only 2% from an African ancestor and there is a complete absence of Amerindian contributions. On the maternal side, 39% have a European Mitochondrial DNA, 33% Amerindian and 28% African MtDNA. This analysis only shows a small fraction of a person's ancestry (the Y Chromosome comes from a single male ancestor and the mtDNA from a single female ancestor, while the contributions of the many other ancestors is not specified)., but it shows that miscigenation in Brazil was directional, between Portuguese males and African and Amerindian females.

Analyzing Black Brazilians' Y chromosome, which comes from male ancestors through paternal line, it was concluded that half (50%) of the Black Brazilian population has at least one male ancestor who came from Europe, 48% has at least one male ancestor who came from Africa and 1.6% has at least one male ancestor who was Native American. Analyzing their mitochondrial DNA, that comes from female ancestors though maternal line, 85% of them have at least a female ancestor who came from Africa, 12.5% have at least a female ancestor who was Native Brazilian and only 2.5% have at least a female ancestor who came from Europe.

As for the complete genetic ancestry of Brazilians, research has shown that it is predominantly European, even among non-White Brazilians. According to another study (autosomal DNA) conducted on a school in the poor periphery of Rio de Janeiro the "pardos" there were found to be on average over 80% European, and the "whites" (who thought of themselves as "very mixed") were found out to carry very little Amerindian and/or African admixtures. "The results of the tests of genomic ancestry are quite different from the self made estimates of European ancestry", say the researchers. In general, the test results showed that European ancestry is far more important than the students thought it would be. The "pardos" for example thought of themselves as 1/3 European, 1/3 African and 1/3 Amerindian before the tests, and yet their ancestry was determined to be at over 80% European.

Another autosomal DNA study, from 2010, also focused on the autosomal contribution (which is about the sum of the ancestors of each individual, the overall picture), found out that almost 80% of the Brazilian genes are of European origin in all regions except in the South where it stands for 90% of them (regardless of census classification). "Ancestry informative SNPs can be useful to estimate individual and population biogeographical ancestry. Brazilian population is characterized by a genetic background of three parental populations (European, African, and Brazilian Native Amerindians) with a wide degree and diverse patterns of admixture. In this work we analyzed the information content of 28 ancestry-informative SNPs into multiplexed panels using three parental population sources (African, Amerindian, and European) to infer the genetic admixture in an urban sample of the five Brazilian geopolitical regions. The SNPs assigned apart the parental populations from each other and thus can be applied for ancestry estimation in a three hybrid admixed population. Data was used to infer genetic ancestry in Brazilians with an admixture model. Pairwise estimates of F(st) among the five Brazilian geopolitical regions suggested little genetic differentiation only between the South and the remaining regions. Estimates of ancestry results are consistent with the heterogeneous genetic profile of Brazilian population, with a major contribution of European ancestry (0.771) followed by African (0.143) and Amerindian contributions (0.085). The described multiplexed SNP panels can be useful tool for bioanthropological studies but it can be mainly valuable to control for spurious results in genetic association studies in admixed populations." The samples came from free of charge paternity test takers, thus as the researchers made it explicit: "the paternity tests were free of charge, the population samples involved people of variable socioeconomic strata, although likely to be leaning slightly towards the ‘‘pardo’’ group".

According to another different study (also autosomal DNA from 2009), European ancestry predominates in the Brazilian population. The Brazilians as a whole, from all regions, and of all complexions, would lie more closely to the European group than to the African populations or to the Mestizos from Mexico, from the genetical point of view. This shows that the genotypes of individuals in a miscigenated population does not necessarily match their phenotype.

According to another autosomal DNA study from 2008, by the University of Brasília (UnB), European ancestry dominates in the whole of Brazil (in all regions), accounting for 65,90% of heritage of the population, followed by the African contribution (24,80%) and the Native American (9,3%).

An autosomal study from 2011 (with nearly almost 1000 samples from all over the country) has also concluded that European ancestry is the predominant ancestry in Brazil, accounting for nearly 70% of the ancestry of the population: "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 In all regions studied, the European ancestry was predominant, with proportions ranging from 60.6% in the Northeast to 77.7% in the South In all regions studied the European ancestry surfaced as uniformly preponderant, with proportions of 69.7%, 60.6%, 73.7% and 77.7%, respectively". The 2011 autosomal study samples came from blood donors (the lowest classes constitute the great majority of blood donors in Brazil ), and also public health institutions personnel and health students. The study showed that Brazilians from different regions are more homogenous than previously thought by some based on the census alone. "Brazilian homogeneity is, therefore, a lot greater between Brazilian regions than within Brazilians region".

According to an often quoted autosomal DNA study (from 2003) focused on the composition of the Brazilian population as a whole, "European contribution is highest in the South (81% to 82%), and lowest in the North (68% to 71%). The African component is lowest in the South (11%), while the highest values are found in the Southeast (18%-20%). Extreme values for the Amerindian fraction were found in the South and Southeast (7%-8%) and North (17%-18%)". The researchers noted the possibility that these conclusions could be skewed because they mostly come from economically well-to-do individuals who have registered for paternity tests. ""But an alternative explanation is that since the bulk of our sample is composed of individuals who could pay for paternity determinations, it may reflect the marked socioeconomic differentials that exist among people of different ethnic extraction in Brazil. Results of the last (year 2000) census of the Brazilian population showed marked economic differences associated with ethnic/color classification. The average monthly income of people self-defined as ‘‘black or brown’’ is about 60.0% (South region) to 51.3% (Southeast) of the amount reported by self-classified ‘‘white’’ persons. Thus, people in a better economic condition are mostly of European extraction, thus at least partly explaining the different proportions observed here and in other samples".

Several other studies have suggested that European ancestry is the main component in all Brazilian regions. A study from 2002 quoted previous and older studies (28. Salzano F M. Interciêência. 1997;22:221––227. 29. Santos S E B, Guerreiro J F. Braz J Genet. 1995;18:311––315. 30. Dornelles C L, Callegari-Jacques S M, Robinson W M, Weimer T A, Franco M H L P, Hickmann A C, Geiger C J, Salzamo F M. Genet Mol Biol. 1999;22:151––161. 31. Krieger H, Morton N E, Mi M P, Azevedo E, Freire-Maia A, Yasuda N. Ann Hum Genet. 1965;29:113––125. ), saying that: "Salzano (28, a study from 1997) calculated for the Northeastern population as a whole, 51% European, 36% African, and 13% Amerindian ancestries whereas in the north, Santos and Guerreiro (29, a study from 1995) obtained 47% European, 12% African, and 41% Amerindian descent, and in the southernmost state of Rio Grande do Sul, Dornelles et al. (30, a study from 1999) calculated 82% European, 7% African, and 11% Amerindian ancestries.