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The Wichí people from Chaco province inhabit the region called Impenetrable Chaqueño, where the climatic conditions are extreme. Besides the scarce communication with the main urban centers, the cultural patterns of the Wichí cause these communities to live in certain degree of isolation. The effect of this situation is an increased genetic differentiation from other populations, as it was observed through autosomal and Y chromosome markers. However, the genetic variation of X chromosome has not been fully analyzed yet. The patterns of allele distribution of different markers of X chromosome can be highly informative in comparative studies, because its special features make this chromosome a potential source to uncover ethnic differences.

The aim of this study was to assess the variation of X chromosome present in the Wichí population living around Misión Nueva Pompeya, in the Chaco province, and to identify particular variation of X-repetitive markers (X-STRs) in Chaco Amerindians. We genotyped Wichí for ten non-coding X-STRs and compared them with a Mocoví population and with published data on individuals coming from European immigration.

We found high homozygote proportion and linkage disequilibrium values for X chromosome in the Wichí population. The Wichí showed to be more distant from non-native people than the Mocoví population analyzed for comparison. We also found certain differences with Mocoví, possibly due to a higher genetic flow of the latter with non-natives. A process of genetic drift seems to be enhanced by the social behavior of the Wichí, since they live appart from other native and non-native groups. The geographic isolation and the extreme environmental conditions can also be considered as major factors contributing to the population differentiation. Although we found no new allele or undescribed variation, the whole pattern of variation for these markers gives the Wichí a particular population identity.