Has hypoxia adaptation in the Ethiopian highlands mirrored that seen in Tibet and the Andes? Is there a genetic definition for an Ashkenazi Jew? These are two questions on human diversity that can now be answered, thanks to new research articles published in this month's Genome Biology.
In the first article, the University of Pennsylvania's Tishkoff lab, in collaboration with Addis Ababa University, sought to identify genetic adaptations to high altitude present in the Amhara people of the Ethiopian Highlands. Two other high altitude populations – in Tibet and the Andes – have previously been studied in this way; obtaining Ethiopian samples, however, proved to be a challenging feat.
A set of strong candidate genes for high altitude selection were identified in the Amhara, whose samples were used both for genotyping and for physiological measurements. As with Tibetan and Andean populations, adaptations targeted the HIF-1 pathway, demonstrating the selective pressure brought about by the risk of hypoxia in high altitude environments. While the three populations share an adaptive pathway in common, the individual genetic changes underlying the hypoxia-resistant phenotype were different in the Ethiopian cohort to those seen in Tibetans or Andeans. This example of convergent evolution suggests that the HIF-1 pathway is an inevitable adaptation in any population under selection pressure for hypoxia.
The definition of what constitutes a Jew is an age-old question without a simple answer. The Ashkenazim are a subpopulation of the Jewish people descended from a small founder population based in Western Europe approximately 1,000 years ago; using the largest Ashkenazi genotyping cohort to date, Todd Lencz (The Feinstein Institute for Medical Research) and colleagues were able to determine a distinct genetic signature that can identify Ashkenazi Jews.
Consistent with previous reports, the article concludes that the founding Ashkenazi population likely included both Levantine Jewish and European Caucasian individuals. However, the results presented by Lencz and colleagues powerfully show that, since the founding event, the level of admixture with "host" European populations (and with other Jewish populations) has been extremely low.
The genetic signature also harbors an enrichment of genes associated with disease pathways known to be overrepresented in the Ashkenazi population, and so will therefore help to unravel the genetic bases by which these conditions (including cystic fibrosis and Usher syndrome) have become prevalent among Ashkenazim.