Studies On Paternal Genetics Of Liqian People From Yongchang County Of Gansu Province, China

Liqian people, officially recognized as Han Chinese by P. R. China, live in some small village located in Yongchang County of Gansu province, China. Many of them have light colored hair and Caucasian features, which are sharply different from Han Chinese and most ethnic minorities. Recent years, Liqian people were well known to all with controversial hypothesis of ancient Roman mercenary origin. In 1955, Homer H. Dubs proposed that some Roman soldiers captured by the Parthians after Crassus's defeat at Carrhae in 53 B.C. were eventually hired as mercenaries by a Hun warlord in the western frontier past the boundaries of the Han Empire and were captured by the Chinese and allowed to form their own city, based on the Roman model. The hypothesis has been adopted by some scholars. It was, however, disputed by many historians. Several decades passed, the hypothesis remains hotly debated. No direct evidence, paternal genetic contribution seems particular necessary. To test this hypothesis, we surveyed more than 12 Y chromosome binary polymorphisms by use of PCR (polymerase chain reaction), PCR-RFLP (restriction fragment length polymorphism), DHPLC (Denaturing High Performance Liquid Chromatography) methods and 12 short tandem repeat (Y-STRs) loci by using Powerplex^? Y system for 227 male individuals representing four Chinese populations: Liqians, Yugurs, Uygur and Tibetans. In comparison with worldwide populations, the following results were obtained.1. Eleven Y-SNP haplogroup and 75 Y-STR haplotype were observed for 87 unrelated Liqian males. At the haplogroup level, the Liqians presented low genetic diversity with a single highest frequent haplogroup O3-M122 (71.3%). When 12 fast-evolving Y-STRs were used, the genetic diversity of Liqians is high than 0.98. In present study, 77% Liqian Y chromosomes were restricted to East Asia. It is unexpected that the frequency of Haplogroup O-M175, an East Asian-specific haplogoup, is relatively higher in Liqian people than that in most populations in North China.2. Principal Component (PC) based on Y-SNPs and multidimensional scaling (MDS) analysis on basis of Y-STRs suggests that the Liqians is closely related to Chinese populations, especially Han Chinese populations, whereas greatly deviate from Central Asian and West Eurasian populations. The positions of populations within some clusters correspond well to their predefined assignments to specific regional groups. One conclusion can also be drawn from these analyses: despite the ascertainment bias in the binary markers, PC result based on Y-SNPs is consistent with MDS result on basis of Y-STRs. In addition, further phylogenetic analysis confirmed the genetic affinity between Liqian and Han Chinese populations.3. By PC and MDS analysis, we found two old populations: Han Chinese and Mongolians, which showed close genetic relationship to Liqians. In subsequent admixture analysis, the two populations were assumed to be parental populations of Liqians, and the Liqians is regarded as hybride population. Admixture proportional analysis suggested that the genetic contribution from Han Chinese amount to 78% in Liqians.4. The Liqians and the Yugurs, regarded as kindred populations with common origins, present underlying genetic difference in Median-joining network and admixture proportional analysis.5. Liqian population show close affinities to its geographic neighbors. This is confirmed in Mantel test (r=0.646, P =0.003), which show a strong and highly significant partial correlation between genetics and geography among population mentioned in our study.6. Statistically, the Liqian showed non-significant genetic difference to Han Chinese in North China, and significant genetic difference to other Eurasian populations.7. When we compare Liqian minimal haplotypes (9 loci "minimal haplotype") with worldwide data in YHRD, most Liqian haplotypes were found in East Asia and South Asia. Only two matches were found in Europe, but they belonged to East Asia-specific Haplogroup O-M122. The incompatible result probably originated from recurrent mutation of fast-evloving Y-STRs.Overall, Roman mercenary origin could not be accepted as a history truth according to paternal genetic variation, and the current Liqian population is more likely to be a subgroup of Chinese majority Han. Our studies provided genetic evidence for the origin of the Liqian people, and inriched to human genetic database. The 12 Y-STR polymorphism markers are highly discriminating in the Chinese Liqian population, and they may be powerful for paternity testing and personal identification.