Genetical-demographic data from two amazonian populations composed of descendants of african slaves: Pacoval and Curiau

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. 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