Mitochondrial Genomes Uncover The Maternal History Of The Pamir Populations

The settlements of high-altitude regions have been a hotspot in human evolutionary genetics.One of the famous plateaus in Central Asia,the Pamirs,are a mountain knot in the heartland of Asia at the junction of the Himalayas and Hindu Kush,Tien Shan,Karakoram,and Kunlun ranges.The average elevation ranges from 2500 to 4500 m.The harsh conditions(e.g.hypoxia,strong ultraviolet radiation,and cold temperature)associated with high altitude make the Pamirs become one of the most challenging areas to human settlement.Due to constraints such as sampling difficulty,the origin of early highlanders as well as their settlement history remains obscure.During the past two decades,mitochondrial DNA(mtDNA)has improved our understanding of genetic diversity and population history in Central Asia.Nevertheless,most previous studies relied on partial mtDNA sequences(i.e.D-loop and certain coding regions).The limited genetic information hampers a fine resolution of mtDNA phylogeny in this region.Only several Central Asian individuals of interest were selected for mtDNA genome sequencing.To date,few reports focusing on the mtDNA genomes of Central Asian populations have been reported.Thus,We have sequenced the complete mtDNA genomes for 382 individuals belonging to eight populations from the Pamirs and surrounding lowlanders based on the Ion Torrent PGM platform.A series population genetic analyses have been performed and can provide valuable insights into the population history in the pamir.The genetic diversity of the populations show that when considering the standard errors,the genetic diversity indexes in Central Asian populations are at similar level with the values observed in populations from East Asia,South Asia,and West Asia.In terms of PhyloTree(Build 17),We classify all the mtDNA sequences into a subset of those typical of the East and the West Eurasians.No basal lineages of macrohaplogroups M,N,and R are observed in our data,suggesting absence of genetic signal of Out-of-Africa dispersal in Central Asia.Central Asian population is a result of admixture between the already differentiated populations of West and East Eurasia.The result of Principle Components Analysis(PCA)reveal that East Asians have closer genetic relationship with Turkic-speaking Kyrgyz,while In-European speaking Tajiks have closer genetic relationship with West Eurasians.The dating of coalescence ages of all shows around 96.07%Central Asian lineages coalesced after the Last Glacial Maximum(LGM),in other words,humans mainly reached Pamir after LGM.Around 73.56%and 22.51%lineages coalesced in 1-10kya and 10-19kya,respectively.Thus,the early Holocene dispersals play dominant roles in shaping the maternal gene pool of Central Asians.Finally,we carried out selective pressure assessments for Pamir population in contrast to other populations.There is no significant differences in both single genes and whole mtDNA genes N/S values between Pamir populations and other populations,except for COX2 which has lower N/S value in Pamir population.These findings show that Pamir population may not have experienced Darwin's positive selection or a classical relaxation of purify selection is at play.