O uso do DNA mitocondrial em quatro estudos envolvendo a ancestralidade de populações americanas nativas e miscigenadas

Abstract

The Americas settling process was initiated in the XVI century and involved an intense process of genetic mixture among three main people: the Native Americans, the European settlers and the African slaves (sub-Sahara). In America as a whole, historical differences in the peopling pattern have directed the genetic formation of the American current populations. In the present work, we have used the DNA mitochondrial variation as a methodology to study four independent works concerning the ancestry of miscegenated and Native American populations.In the first study, we investigate the maternal ancestry of black individuals who live in the city of São Paulo. Our aim was to study the phylogeography of the African mitochondrial lineages present in this sample. The methodology used was the sequencing of the HVRI region of the mtDNA and RFLP analysis. The results have showed that 85% of the mitochondrial lineages had African origin (sub-Sahara), 11.7% of them were Amerindian/Asiatic, 2.5% European and 0.8% North African. The Main component Analysis and the Bayesian analysis of the population structure disclosed the existence of a considerable genetic structure among the three investigated African regions. In both analyses, the individuals from São Paulo with African maternal ancestry had been grouped closer to the Central-West Africa cluster. This region has also revealed a larger contribution (0.450) for the São Paulo sample, when a quantitative analysis was concluded. The results achieved corroborate with the historical data about the origin of slaves who were brought to Southeastern ports of Brazil. In Chapter II we have studied the occurrence of genetic flow by sexual bias on a North American Caucasian population. This phenomenon was common during the formation process of the Latin populations and was recently observed between African Americans. Therefore, we have retrieved HVRI sequences of mitochondrial DNA for the American Caucasian group available in FBI mtDNA population database. The results showed that only 3.1% of Caucasians sequences in U.S.A. had African and/or Amerindian origin, which was unexpected. These discrepancies can be explained by divergent social practices existing between the U.S.A. and Latin America, in which racial categorization of children allow individuals of the same color to belong to distinct races.In chapter III, we have retrieved mitochondrial DNA samples of ancient teeth from Botocudo Indians with the purpose to compare their lineages with those obtained from the Queixadinha population. This community lives nowadays in a place once occupied by the Botocudos in the XIX century. Thus, it has been proposed that among the mitochondrial lineages from Queixadinha there were genetic signatures of this indians (Parra, 2003). To achieve this task, we analysed twelve Botocudos teeth and for three of them we obtained complete HVRI mitochondrial sequences. No lineage sharing was observed between both populations. However, the existence of an Amerindian A individual among the Botocudos was indicative of a larger genetic diversity in this indians than Queixadinha. It is a signal that the genetic drift is a restrictive factor for the use of the metodology proposed for recovering extinct Amerindian lineages present in the genetic pool of Brazilian current population (Parra, 2003).Finally, we have tested an hypothesis of a possible positive conection between cleft lip with or without the palate (CL/P) and Amerindian ancestry. This hypothesis was proposed by Vieira et al (2002) who have found a strong association between Amerindian ancestry (haplogroup D) and CL/P in South America populations. In order to validate the association proposed by Vieira et al., in our study we have made an analysis of the Amerindian ancestry of two sample groups: individuals from ECLAMC and individuals from Brazil only. However, our results have not confirmed such association and we suggest that the higher rate of Amerindian ancestry as well as the excess of lineages D in CL/P cases observed by Vieira et al. is, in fact, sampling artifacts. Thus, we criticize the association made by the authors between mitochondrial and autossomal ancestry.