Abstract
Since their arrival in the Tibetan Plateau during the Neolithic Age, Tibetans have been well-adapted to extreme environmental conditions and possess genetic variation that reflect their living environment and migratory history. To investigate the origin of Tibetans and the genetic basis of adaptation in a rigorous environment, we genotyped 30 Tibetan individuals with more than one million SNP markers. Our findings suggested that Tibetans, together with the Yi people, were descendants of Tibeto-Burmans who diverged from ancient settlers of East Asia. The valleys of the Hengduan Mountain range may be a major migration route. We also identified a set of positively-selected genes that belong to functional classes of the embryonic, female gonad, and blood vessel developments, as well as response to hypoxia. Most of these genes were highly correlated with population-specific and beneficial phenotypes, such as high infant survival rate and the absence of chronic mountain sickness.
Highlights
Humans first reached the Tibetan Plateau during the Last Glacial Maximum (22–8 kya) [1], and modern Tibetans can be traced back to Neolithic immigrants based on evidence found in the Y chromosome [2] and mitochondrial DNA [3]
Tibetans appeared to share the majority of their ancestry with East Asian (EA) populations
Our population genetic structure analyses suggested that Tibetans share the common ancestors with East Asian populations, but not Central/South Asian populations who settled on the western and southern side of Himalayas
Summary
Humans first reached the Tibetan Plateau during the Last Glacial Maximum (22–8 kya) [1], and modern Tibetans can be traced back to Neolithic immigrants based on evidence found in the Y chromosome [2] and mitochondrial DNA [3]. The exact origin of modern Tibetans has been widely debated due to varying and conflicting evidence from archaeology, historical records, linguistics, and genetics [3,4]. Previous studies have suggested, based on genetic evidence, two distinct possibilities for whom the ancestors of modern Tibetans were: people who lived in the upper and middle Yellow River basin [3,5] and Northern Asian populations [6]. The Tibetan Plateau is unique in its high absolute elevation and low temperature. Tibetans have lived on the plateau for tens of thousands of years and adapted to the high-altitude environment better than other populations. Tibetans exhibit many biological features in common with other high-altitude mammalian species (such as antelopes and pigs), including absence of chronic mountain sickness (CMS), thin-walled pulmonary vascular structure, and high blood flow [8]; all these phenotypes are highly correlated with physiological responses to low oxygen concentration in the air, which facilitate uninterrupted oxygen-processing and the up-regulation of erythropoiesis and angiogenesis to allow for more efficient oxygen utilization
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