Research paper
Genetic polymorphism and population structure of Torghut Mongols and comparison with a Mongolian population 3000 kilometers away

https://doi.org/10.1016/j.fsigen.2019.07.017Get rights and content

Highlights

  • Both the Torghut and Jalaid Mongols have population-specific alleles.

  • The STRs and SNPs analyzed here could be employed in forensic applications.

  • The Torghut and Jalaid Mongols are closely related by their genetic background.

  • Interpopulation comparisons revealed genetic differences between the two populations.

Abstract

Mongolians played a pivotal role in shaping the culture and genetic architecture of modern Eurasia through the rapid expansion of the Mongol Empire in the 13th century. While the historical aspects of the Mongolian Empire are well documented, research on the genetic variations among Mongolian populations is still insufficient. In this study, we examined the genetic diversity of 70 Torghut Mongols residing in the Ili region of China compared with 88 Jalaid Mongols residing 3000 km away. Over 200 forensically relevant genetic markers, including autosomal short tandem repeats (A-STRs), X chromosomal STRs (X-STRs), Y chromosomal STRs (Y-STRs), identity-informative single nucleotide polymorphisms (iiSNPs), ancestry-informative SNPs (aiSNPs), and phenotype-informative SNPs (piSNPs), were genotyped to uncover the genetic polymorphism of the Torghut Mongols. The STR genotyping results showed that 80 alleles (39 A-STRs, 25 Y-STRs, and 16 X-STRs; 14.4% of 554 alleles) identified in Torghut Mongols were not identified in Jalaid Mongols, while 155 alleles (84 A-STRs, 59 Y-STRs and 12 X-STRs; 24.6% of 630 alleles) identified in Jalaid Mongols were not observed in Torghut Mongols. Calculation of the forensic parameters demonstrated that the STRs and SNPs analyzed here could be employed in forensic applications. Interpopulation comparisons via principal component analysis (PCA), phylogenetic tree, and STRUCTURE analysis showed that the two Mongolian populations were closely related by their genetic background, although genetic differences were also discovered. When both the sequence-based A-STRs and iiSNPs were included in the STRUCTURE analysis, the Torghut population was more similar to the Uyghur population than to Jalaid Mongols, indicating certain population structure differences between the two Mongolian populations. The Y-DNA haplogroup prediction showed that although haplogroup C (C2-M217) was dominant in both Mongolian populations, haplogroup O2-M122 was rarely presented in Torghut Mongols, which differentiated the Torghut Mongols from the other Mongolian populations. This study not only uncovered the genetic features of the two Mongolian tribes, providing valuable frequency data for forensic applications, but the genetic patterns of the two Mongolian populations also provide a genetic evidence that the Torghut Mongols may have developed via the gradual intermixing of nomadic groups of Mongol and Turkic origin, as recorded in historical records. This study also highlighted the importance of building regional reference databases that consider both ethnic and geographic location information, instead of a more universal reference database, for forensic applications.

Introduction

Mongols (also called Mongolians) founded the largest continental empire in the history of the world in the 13th century [1]. The territorial expansion of the Mongol Empire facilitated cultural and trade exchanges between Asia and Europe. Genetic studies on current Mongolian populations have not only indicated that most Mongolian tribes were genetically similar to both East Asian and Siberian populations but also revealed the remarkable effects on the genetic structure of Eurasians by the Mongol Empire [[2], [3], [4], [5], [6], [7]]. Among these studies, the distribution of male genetic lineages based on Y-chromosome have provided both interesting and controversial insights into the paternal genealogy of the Mongols and populations in central Asia [3, [6], [7], [8], [9], [10], [11], [12]]. A study by Zerjal et al. suggested that about 8% of men from a large part of Asia share one specific Y-chromosomal haplotype, carried by likely descendants of Genghis Khan of the Mongol empire [3]. Although this Y chromosome haplotype was called the “star cluster” and considered as evidence of social selection on population genetic structure, the results was deduced with little genealogical support, and the star cluster was later found to be also dominant in some Kazakh tribes that are not directly related to Chinggis Khan [11]. Recent studies pointed out the star cluster as part of the founder paternal lineages of all Mongolic-speaking populations, rather than Genghis Khan himself or his relatives [12].

Today, approximately 10–11 million Mongolians live in China (mainly in the Inner Mongolia Autonomous Region and Xinjiang Autonomous Region), Mongolia, Russia and other places around the world. Mongols are bonded together by their own life style, culture, and language but comprise diverse nomadic tribes. Geographically, the Mongols include the Khalkha Mongols, Buryats, Oirats (Western Mongols) and the Southern Mongols [13]. The latter comprises Baarin, Chahar, Horqin, Jalaid, Jaruud and many other tribes. Although genetic studies have been conducted on Mongolians for years, many studies sampled based on administrative region, considered the Mongol ethnicity as one unit and compare it with other ethnic groups, thereby ignoring the potential genetic diversity among different tribes or within the tribes [14]. Thus, for multiorigin ethnicities such as Mongols, it is worth conducting a population analysis based on more DNA markers in the different subpopulations to clarify the patterns of genetic diversity and understand the dispersal and demographic history of the ethnic group. These data would complement ethnographic, historical, and linguistic evidence about the origins and expansion of these populations.

Once, the Oirats or Western Mongols was the most powerful group of tribes after the collapse of the Mongol Empire but was less studied compare to Khalkha Mongols and the Southern Mongols [13]. The Torghut clan is one of four major subgroups of the Western Mongols. Historically, they descended from the Keraites (also Kereit or Khereid), who are one of the Turco-Mongol tribal confederations that probably formed by the gradual intermixing of nomadic groups of Mongol and Turkic origin during the 12th century [13,15]. To avoid wars, the majority of the Torghuts moved west to the Volga region in 1628, and after almost 150 years, in early 1771, approximately 0.07 million Torghuts migrated back to their hometown, the Ili region of China (Xinjiang) [16,17]. This was one of the last large-scale migrations in modern human history, and the migration routes of the Torghut Mongols and their residing places after migration are shown in Fig. 1. Today, the number of Torghut descendants is approximately 0.1 million in China, with most of them still residing in Xinjiang and some in western Inner Mongolia. Most modern Torghuts speak Oirat dialect of Mongolian language, and some still maintain nomadic lifestyle. Although the Torghut tribe is one of the key groups of Mongolian ethnicity, little is known about their genetic background or their relationship with other Mongolian populations due to the paucity of genetic data. Whether they have some Turkic ancestry has not been genetically studied. In addition, the uncovered genetic data will also be valuable for applications in human identity testing and population disease studies.

With the development of massively parallel sequencing (MPS), multiple genetic markers can be genotyped simultaneously [18,19]. At present, most previous studies on Mongolian populations involved limited number of molecular markers (usually 10˜ to 30˜) with few overlapped markers to conduct comparative studies [3,6,14,20,21]. A simultaneous analysis of Y-chromosomal, X-chromosomal and autosomal loci in Mongolians will not only expand our understanding of genetics feature of Mongolians but also help to conduct a comparative genomic study. In this study, we examined the genetic diversity of Torghut Mongols residing in the Ili region of Xinjiang based on autosomal short tandem repeats (A-STRs), X chromosomal STRs (X-STRs), Y chromosomal STRs (Y-STRs), identity-informative single nucleotide polymorphisms (iiSNPs), ancestry-informative SNPs (aiSNPs), and phenotype-informative SNPs (piSNPs). Meanwhile, another Mongolian population, the Jalaid Mongols, belonging to the Southern Mongols and residing 3000 km away from the Torghuts, was also genotyped simultaneously to study the genetic diversity among different tribes. The allele frequencies and forensic parameters were calculated for both populations, and comparisons between these two populations and with other populations were performed.

Section snippets

DNA samples

A total of 158 unrelated individuals, 70 Torghut Mongolians from the Xinjiang Autonomous Region (30 females and 40 males) and 88 Jalaid Mongolians from the Inner Mongolia Autonomous Region (25 females and 63 males) were sampled and genotyped (Supplementary Table S1). The geographical locations of the sampled populations are shown in Fig. 1. Peripheral blood samples were collected and dried on an FTA card (approximately 200 μL of blood). A genealogical history was collected from each donor for

Results and discussion

In this study, 70 individuals from a Mongol tribe, the Torghut Mongols, were genotyped using the ForenSeq™ DNA Signature Prep Kit, and genetic data from over 200 molecular markers were obtained. Eighty-eight individuals from another Mongolian population residing 3000 km away were also genotyped for comparison. The forensic efficiency of the genetic markers in the ForenSeq™ DNA Signature Prep Kit for application in the two Mongolian populations was evaluated and interpopulation comparisons were

Conclusion

In summary, we provided the first genetic polymorphism data of 70 unrelated Torghut Mongols by genotyping forensic genetic markers using the ForenSeq™ DNA Signature Prep panel. Allele frequencies were reported, and the forensic parameters were assessed for not only the Torghut Mongols but also for Jalaid Mongols. The results demonstrated that the STRs and SNPs analyzed here were highly polymorphic in these populations and could be employed in forensic applications. The interpopulation

Declaration of Competing Interest

The authors declare that they have no conflicts of interest.

Acknowledgements

This study was funded by the National Natural Science Foundation of China (81801878, 81671873), the Natural Science Foundation of Guangdong Province (2018A030313413) and the Fundamental Research Funds for the Central Universities (17ykpy10).

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