RESUMEN
Five hundred years after the arrival of the first Portuguese colonizers, the Brazilian Amazonia is predominantly inhabited by mestizos, formed by the admixture among three main ethnic groups (Amerindians, Europeans and Africans). On the other hand, the region is the habitat of the last culturally autonomous indigenous tribes in Brazil, most of them showing little (<5 percent) or no mixture with other ethnic groups, and also includes several communities founded by escaped African slaves, named quilombos, some of which still remains relatively isolated. Genetical (classic genetic polymorphisms, nuclear DNA and the mtDNA polymorphisms) and genetical-demographic (estimates of interethnic admixture) data have been obtained for these human groups. Estimates of interethnic admixture for urban populations show average values of 41 percent of Indigenous contribution, 12 percent of African contribution and 47 percent of European contribution, the data showing an increase of Indigenous contribution in the direction of Belém to Manaus, followed by the reduction of the African contribution in the same direction. On the other hand, Y-DNA and mtDNA data obtained for the population of Belém demonstrate that the contribution of indigenous females to the formation of the population was 10 times higher than that of indigenous men. Studies performed in Afro-Brazilian communities indicate that although African slaves imported in the northern region have been predominantly from Bantu-speaking Africa, the number of slaves from West Africa, particularly from the Atlantic West, brought to northern Brazil may have been higher than that indicated by historical records. With respect to Amerinds, analysis of classical genetic markers and DNA polymorphisms (tandemly repeated loci) in several Amerindian populations do not coincide, the former indicating that tribes of the northern margin of the Amazon river are less differentiated than those from the southern margin, and that the within-stock genetic differentiation for the Tupi group is higher than that between-stock.