The formation of the Brazilian Amazonian population has historically involved three main ethnic groups, Amerindian, African and European. This has resulted in genetic investigations having been carried out using classical polymorphisms and molecular markers. To better understand the genetic variability and the micro-evolutionary processes acting in human groups in the Brazilian Amazon region we used mitochondrial DNA to investigate 159 maternally unrelated individuals from five Amazonian African-descendant communities. The mitochondrial lineage distribution indicated a contribution of 50.2% from Africans (L0, L1, L2, and L3), 46.6% from Amerindians (haplogroups A, B, C and D) and a small European contribution of 1.3%. These results indicated high genetic diversity in the Amerindian and African lineage groups, suggesting that the Brazilian Amazonian African-descendant populations reflect a possible population amalgamation of Amerindian women from different Amazonian indigenous tribes and African women from different geographic regions of Africa who had been brought to Brazil as slaves. The present study partially mapped the historical biological and social interactions that had occurred during the formation and expansion of Amazonian African-descendant communities.

Five loci (vWA1, F13A1, D12S67, Apo-B and D1S80) were investigated by polyacrylamide gel electrophoresis followed by silver staining in a sample of 177 individuals from the population of São Luís, State of Maranhão, Brazil. A total of 70 different alleles were identified. A statistically significant deviation from the Hardy-Weinberg equilibrium was observed in a single locus (F13A1, p = 0.0075). The average heterozygosity (H) was estimated at 77.7%, the mean number of alleles per locus as 14. The PD (capacity of genotype differentiation at each locus) ranged from 88.9% (vWA1) to 96.7% (F13A1). The combined PE (power of exclusion) of these five loci was 99.8%. In terms of racial admixture (42% European, 39% Indian, and 19% African Black ancestry), São Luís presented an estimate similar to Belém, another trihybrid Amazonian population.

A região amazônica brasileira abriga diversas comunidades formadas por descendentes de escravos africanos, algumas das quais ainda relativamente isoladas. Nós estudamos duas dessas comunidades (Pacoval e Curiau), localizadas na área rural do município de Alenquer, Pará, e na região metropolitana de Macapá, Amapá, respectivamente. Entre os 12 loci investigados, alelos considerados como marcadores de ancestralidade africana, tais como HBB*S, HBB*C, TF*D1, HP*2M, ABO*B, RH*D- e CA2*2, foram encontrados com freqüências elevadas, de acordo com o esperado para populações com origem predominantemente africana. As estimativas de mistura racial indicaram que o percentual de contribuição africana em Curiau (74%) é maior do que em Pacoval (44%) e que em Curiau não foi detectada mistura com indígenas. As estimativas de ancestralidade africana estão de acordo com o grau de isolamento e com a mobilidade das comunidade estudadas. Pacoval apresenta um elevado percentual de imigrantes entre os pais e avós dos individuos estudados, enquanto que a comunidade de Curiau, apesar de situada na região metropolitana de Macapá, apresenta uma pequena proporção de imigrantes, sugerindo a existência de uma barreira relativamente forte contra a mistura interétnica. A análise dos dados genéticos foi também efetuada em sub-amostras constituídas apenas por indivíduos cujos pais e avós nasceram na localidade em estudo e que provavelmente representam essas populações duas gerações atrás. Os resultados indicaram que a mistura com não-negros nas duas populações não é um evento recente.

The Amazon region of Brazil includes communities founded by escaped slaves, some of which still remain relatively isolated. We studied two such Afro-Brazilian communities (Pacoval and Curiau), in the rural area of Alenquer, Pará, and in the metropolitan region of Macapá, Amapá, respectively. Among 12 blood loci, alleles considered as markers of African ancestry, such as HBB*S, HBB*C, TF*D1, HP*2M, ABO*B, RH*D-, and CA2*2 were found at frequencies that are expected for populations with a predominantly African origin. Estimates of interethnic admixture indicated that the degree of the African component in Curiau (74%) is higher than that of Pacoval (44%); an Amerindian contribution was not detected in Curiau. Estimated values of African ancestry fit well with the degree of isolation and mobility of the communities. Pacoval exhibited a high proportion of immigrants among the parents and grandparents of the individuals studied, whereas persons living in Curiau exhibited a low level of mobility, despite its location in the metropolitan area of Macapá city, suggesting a relatively strong barrier against the interethnic admixture in this population. In addition, analysis of genetic data in a sub-sample consisting of individuals whose parents and grandparents were born in the study site, and that probably represents the populations two generations ago, indicated that gene flow from non-black people is not a recent event in both populations.