English: Maps of principal component analysis (PCA) based on mtDNA and Y-Chromosome haplogroup frequencies among Sherpas, Tibetans and other Asian populations. We explored the genetic relationship between Sherpas and other Asian populations, and principal component analysis (PCA) of both mtDNA and Y chromosome haplotype frequencies displayed a close relationship between Sherpas and Tibetans (Fig. A,B). In particular, the PCA map of the Y chromosome shows Sherpas mingled together with Tibetan populations and forming a separate cluster from other Asian populations (Fig. B). The PCA map of mtDNA further places the Sherpas relatively closer to Tibetans compared to other Asian populations but form a separate cluster, implying a shallow divergence from Tibetans likely due to the recent expansions of the two Sherpa-specific mtDNA sub-haplogroups (A15c1 and C4a3b1) (Fig. A). By contrast, non-Sherpa Nepalese are only distantly related to Sherpas, clustering with populations from the Indian subcontinent and East Asia, suggesting limited gene flows between Sherpas and non-Sherpas in the markedly small area of Nepal nestled between India and China.