Genetic admixture in Brazil

We review studies from our laboratories using different molecular tools to characterize the Amerindian, European and African ancestry of Brazilians. Initially we used uniparental DNA markers to investigate the contribution of distinct Y chromosome and mitochondrial DNA lineages to present-day populations. High levels of genetic admixture and strong directional mating between European males and Amerindian and African females were unraveled. We next analyzed different types of biparental autosomal polymorphisms. Especially useful was a set of 40 insertion-deletion polymorphisms (indels) that when studied worldwide proved exquisitely sensitive in discriminating between Amerindians, Europeans and Sub-Saharan Africans. When applied to the study of Brazilians these markers confirmed extensive genomic admixture. We then studied ancestry differences in different regions by statistically controlling them to eliminate color considerations. The European ancestry was predominant in all regions studied, with proportions ranging from 60.6% in the Northeast to 77.7% in the South. We propose that the immigration of 6 million Europeans to Brazil in the 19th and 20th centuries is in large part responsible for dissipating previous ancestry dissimilarities that reflected region-specific population histories. Brazilians should be assessed individually, as 210 million human beings, and not as members of specific regions or color groups.