- Dec 2017
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www.scienceintheclassroom.org www.scienceintheclassroom.org
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These results suggest that high-altitude adaptation in Tibetans has resulted from local positive selection on several distinct genes.
The presence of the hapolotypes discovered by the XP-EHH and iHS assays are the result of positive selection.
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The strong and significant association between Hb concentration and haplotype variation at EGLN1 and PPARAprovides evidence of a genetic contribution to a form of high-altitude adaptation that appears to be unique to Tibetan populations.
The variations in the PPARA and EGLN1 genes seen in the Tibetan highlanders correlate to decreased hemoglobin levels. The decreased hemoglobin levels in the Tibetan inhabitants that is negatively correlated to hemoglobin concentration provides genetic evidence for high altitude adaptation.
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Each additional copy of an advantageous haplotype at either locus decreases Hb concentration by ~1.7 g/dl on average
Having the adapted versions of the genes EGLN1 and PPARA decreased the amount of hemoglobin in a Tibetan highlander in increasing amount as multiple copies of the haplotype are seen. For example; one copy of the Tibetan EGLN1 gene slightly decreases the hemoglobin concentration, but two copies of the Tibetan EGLN1 gene significantly reduces hemoglobin concentration.
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On average, the XP-EHH and iHS intersections contained 2.7 and 1.4 genes, respectively, significantly fewer than the six (P < 0.05) and five (P < 0.01) genes actually observed.
The researchers resampled and calculated the genes undergoing positive selection. These genes were originally found using the XP-EHH and iHS test. It was discovered that a decrease in gene numbers found by both tests (from 6 to 2.7 and from 5 to 1.4).
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