Avaliação de diferentes estratégias na determinação da ancestralidade genética e sua aplicação no estudo de populações nativas e miscigenadas da América do Sul

Abstract

Human populations have different patterns of genetic diversity, which are reflected in a wide variation between individuals. In addition to the existing variation between populations from different continents, there are patterns of intracontinental diversity related to miscegenation events among distant populations, namely from different continents. This type of variation that resulted from the contribution of different ancestral populations has been assessed on the basis of the so called ancestry informative markers (AIMs). In this thesis, Indel markers, with different levels of diversity and variation intra and inter-population, have been used, aiming (i) to evaluate different strategies in the determination of populations ancestry and (ii) to establish ancestry patterns in mixed populations from South America. In first part of this study, ancestry values were estimated and compared in father-mother-son trios and duos of siblings. However, comparison of father-mother-child trios and in pairs of siblings showed not to be suitable strategy to evaluate ancestry when groups of markers with low capacity of differentiation are used, since the estimated values tend to converge in the same central value (one third for each of the contributions, namely African, European and Native American). Moreover, the randomness of the differences between expected and observed values produced by groups of markers with high ability to differentiate ancestral populations, proved the usefulness of comparing ancestry values among members of family groups. In this case, the increase in the number of markers analysed led to a decrease of the difference between the expected and observed values of ancestry, and it was found that the addition of markers with low power of differentiation, to a group of AIMs, increases the accuracy of the estimates. In the second stage of this work, 46 AIM were analysed in Bolivian and Colombian population samples, and used to determine the corresponding ancestry profiles. In Bolivia, both in Chuquisaca and La Paz, a high native ancestry was found in spite of Chuquisaca have a greater European influence. In these two Bolivian population samples, a significant association between AIMs and Y chromosome markers was further observed, demonstrating the presence of substructure at both the inter and intrapopulation levels. The evaluation of five Native American groups in Colombia showed different patterns of European and African genetic admixture. While the indigenous groups Embera-Chami, Motilón-Barí and Guainia have very low levels of non-native genes, the native population of the Cauca region and the Pijao have high proportions of European and, to a lesser extent, African influx. On the other hand, admixed Colombian samples showed different patterns of ancestry, which vary with their geographic locations. The population of the Amazon region was characterized by greater Native ancestry; the African ancestry prevailsin the Pacific region; while the European component was the highest in the Andes and Orinoco. The high genetic variation observed within and between Colombian populations is compatible with the recent admixture events between well differentiated populations, and the presence of population s stratification along the territory. In summary, this work provided important information on the definition of studies related to genetic ancestry and to deepen the knowledge of the genetic structure of some populations in South America influenced by admixture phenomena.