February 28, 2006

Brazilian Y chromosomes

One of the lessons from the following paper is that microsatellite diversity does not always point to the correct direction of migration. If we knew nothing about Brazilians and Portuguese, we might be inclined to attribute the lower Portuguese genetic diversity to migration from Brazil to Portugal, even though the opposite is the case.

Genetica Volume 126, Numbers 1-2 Pages: 251 - 260

Y Chromosome Diversity in Brazilians: Switching Perspectives from Slow to Fast Evolving Markers

Denise R. Carvalho-Silva et al.

We have previously shown that the Y chromosomes of ‘white’ Brazilians have their immediate geographical origin in Europe, with low frequency of sub-Saharan African chromosomes and virtual absence of Amerindian contribution. The typing of slow evolving polymorphisms on the Y chromosome also revealed no differences between Brazilians and Portuguese, the bulk of European immigrants to Brazil, and even among Brazilians from distinct regions of Brazil, the latter being in sharp contrast with mtDNA data. In order to test if the lack of differentiation is a sex-biased and not a marker-biased phenomenon, we decided to study faster evolving Y chromosome markers in samples from Brazil and Portugal previously studied. The population structure revealed by this work confirmed that there were indeed no significant differences between Brazil and Portugal and no population differentiation within the four geographical regions of Brazil, suggesting that this phenomenon is unrelated to the nature of the markers typed. Nevertheless the fast evolving markers did uncover a higher within population diversity in Brazil than Portugal, which could be explained by the input of diverse European Y chromosomes carried by several migration waves to Brazil. Our present data highlight the significance of typing and combining Y markers that evolve according to distinct mutational paces to usefully assess the levels of diversity in a given population, and can be applied in the study of populations derived from distinct geographical origins such as the Brazilians.


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