Understanding admixture and building an admixture mapping panel
Studying admixture is important from a historical and anthropological perspective. Migration of individuals and populations (and subsequent mixing) has always played an important role in the evolutionary history of humans. Since the XVth century, these migrations have occurred at a more global scale. This is particularly the case for the Americas. Here, populations that were previously isolated for generations came into contact and many persons currently living in North, Central and South America can trace their ancestry to different continents. We can reconstruct and interpret this history of migrations and admixture using genetic markers. A very complete perspective can be obtained when analyzing autosomal markers, maternally transmitted mtDNA markers and Y-chromosome specific markers, which are transmitted from fathers to sons. In many cases, the maternal and paternal admixture histories are remarkably different, so including mtDNA and Y-chromosome markers can provide a much better picture than that offered by the autosomal markers. Thus, using genetic markers we can reconstruct history at the individual and population level, even in the absence of a historical record.
In addition to the role that these
studies play in understanding human migrations, it is possible
to exploit the recent history of admixture to map disease genes, using a
method known as admixture
mapping. Admixture mapping is particularly useful to study
diseases having large differences in prevalence between major population groups,
such as Type 2 Diabetes or Hypertension, among others. One of the advantages of
admixture mapping over alternative methods is that a substantially smaller panel
of markers will be required. However, these markers have to be carefully
selected. Ideally, the best markers are those showing high frequency differences
between the major population groups that were involved in the admixture process.
Due to the recent origin of our species, most of the genetic markers show low
frequency differences between human populations. Only a small percentage of the
markers are informative for admixture mapping. In collaboration with Mark Shriver, from Penn
State University, and Paul
McKeigue, from the
University of Edinburgh, among others, we have developed a genome-wide admixture
mapping panel for Hispanic/Latino populations, including more than 2,000
informative markers.