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 per cent) is higher than that of Pacoval (44 per cent); 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.

Migration and ethnic change in an admixed population from the Amazon region (Santarém, Pará)

Dados genéticos e demográficos da populaçäo de Santarém, PA, foram analisados. Oitenta e dois por cento dos indivíduos estudados nasceram no Estado do Pará e 11,7 por cento dos imigrantes nasceram na regiäo Nordeste do Brasil. A análise da migraçäo individual média, distância marital média, distância genitor-prole e índice de exogamia identificou uma elevada mobilidade populacional. Alelos característicos dos três principais grupos étnicos foram encontrados, como BCHE*A (caucasóides) ALB*Maku (indígenas) e HBB*S e HBB*C (negros). As proporçöes de ancestralidade negra, índia e branca foram estimadas em 28 por cento, 35 por cento e 37 por cento, respectivamente. Condiderando-se o local de nascimento dos avós, a presença de uma subpopulaçäo pôde ser observada (nativos de Santarém). As proporçöes de ancestralidade negra e índia foram de 11 por cento e 52 por cento respectivamente, significantemente diferentes da amostra total. A estratégia usada, portanto, mostrou-se eficiente para a caracterizaçäo dos fatores responsáveis pela estrutura genético-demográfica desta populaçäo.