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Latin American Populations Contain Genetic Clues About Regional History

NEW YORK (GenomeWeb News) – A new study is revealing the way history — particularly the arrival of Europeans to the New World — shaped the genetic diversity of Latin American countries.
 
An international team of researchers analyzed autosomal and X-chromosome microsatellites found in more than a dozen Latin American populations. Their results, published online today in the journal PLoS Genetics, suggest that there are differences in the relative amounts of Native American and European ancestry related to the size and structure of pre-Columbian populations. In addition, many Latin American populations studied apparently descended from European men and Native or African women.
 
In general, admixture mapping is a method for investigating genetic variation in populations that have descended from recently mixed populations. Because individuals in these so-called admixed populations carry genes from both original populations, their genetics provides clues about both ancestral populations.
 
“This approach is potentially more powerful and economical than high-density whole-genome association studies and should also allow the identification of trait-related genetic variants that are fixed in one of the parental populations,” the authors wrote. “Ideally, the application of admixture mapping should build on knowledge regarding the genetic makeup of the admixed population as well as of the specific ancestral populations that contributed to the admixture.”
 
In a first step towards applying such admixture mapping to Latin American populations, senior author Andrés Ruiz-Linares, a biologist at University College London, and his colleagues did a genome-wide characterization of admixed Latin American populations, dubbed Mestizos, found in regions where European and Native American populations mixed during European colonization.
 
To do this, they analyzed 678 autosomal and 29 X-linked chromosome microsatellites using samples from 249 unrelated individuals from 13 Mestizo populations — all urban centers — in seven countries. The samples were originally collected for population and/or disease association studies. They also analyzed data on 160 Europeans, 123 Africans, and 463 Native Americans from 26 populations that was collected for previously published papers or as part of the HGDP-CEPH Human Genome Diversity Cell Line Panel.
 
Using two software programs, the researchers did admixture analysis allowing them to estimate the relative contribution of different ancestral populations to current populations. Based on autosomal data, the researchers found the relative contribution of Native American ancestry varied from roughly 20 percent to 70 percent, depending on the location.
 
In regions that had large Native populations before the arrival of Europeans, such as Salta, Argentina, the population retained a great deal of its Native American ancestry. On the other hand, areas that had small Native American populations in pre-Columbian times tend to have high European ancestry now. There were very low levels of African ancestry — less than five percent — in most of the populations studied.
 
In general, X-chromosome data tended to indicate higher levels of African and Native American ancestry, suggesting an admixture pattern involving African or Native American women and European men.
 
The authors noted that such studies can be confounded by the fact that it’s difficult to know for sure which ancestral populations were involved in admixed populations. Still, they’re hopeful that the study will contribute to future admixture mapping studies, particularly those looking at potential differences in disease-related genes between Latin American, Native American, and European populations.
 
“[T]his initial genome-wide analysis of admixture across Latin American has revealed a hitherto undetected differentiation of the Native American ancestry in Mestizos,” the authors wrote. “This fact, together with the extensive variation observed in rates of admixture across populations, and sometimes also between individuals within populations, needs to be considered when designing admixture mapping studies in specific Latin American populations.”

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