Y-chromosome haplotypes and clan structure of the Sherpa of the Solukhumbu (Nepal): preliminary ethnogenetic considerations

Abstract

The present-day Sherpa are thought to descend from a small number of ancestors that settled in Nepal several centuries ago, coming from the Eastern Tibetan region of Kham. A generally accepted ethnographic theory involves the out-of-Kham migration of four proto-clans between the 15th and 16th centuries. Traditional Sherpa society is still divided into clans, called ru, which are patrilin-early transmitted. Ru therefore roughly correspond to the surnames of Western societies: males of the same ru are expected to share identical Y-chromosome haplotypes. However, multiple origins of ru and/or frequent gene flow of male lineages from neighbouring populations can complicate the genealogical structure. In the present work, 25 male Sherpas of the Solukhumbu district were typed for the 17 Y-chromosomal short tandem repeats included in the AmpFlSTR® Yfiler™ kit. Seventeen different haplotypes were found; 12 were unique. A phylogenetic tree was then drawn from the pairwise mutational distance matrix with a neighbour-joining algorithm. Branching reliability was also assessed through bootstrap analysis. Two macro-clusters of haplotypes were found, ascribable on the whole to two out of four of the presumed Tibetan proto-ru, the Thimmi and the Minyagpa. However, the Minyagpa macro-cluster was found to be bipartite in terms of haplogroups, being composed by two distinct haplotype clusters. Clustering of the contributors by birthplace was also performed, suggesting a differential ru spatial distribution between upper Khumbu and lower Solu. Khumbu seems predominantly populated by newer clans and putative descendants of the Thimmi proto-ru, whereas Solu is mostly inhabited by members of the Minyagpa proto-ru.