Dissection Of Genetic Relationship Between Two Daic Populations-Zhuang And Li Based On MtDNA

Background and ObjectiveIt is well known that China has a vast territory and has many nationalities. The differences between different races, different groups of the same ethnicity, and different populations, mainly due to their genetic materials-DNA molecular differences. More and more genetic researches have been conducted to discover mtDNA genetic structure of human group to trace the history of ancient population evolution, separation, migration and amalgamation. Mitochondrial DNA has proven to be a very effective genetic differentiation markers to study the genetic relationship between human groups and groups within, because of its own specific genetic characteristics, ie maternal inheritance, lack of recombination, the high variability of evolution rate.Zhuang and Li population are two closely original minorities that mainly inhabit southern China.Zhuang is the largest minority population in China, about 1,600 million, of which 1,500 million people living in Guangxi Zhuang Autonomous Region. According to historical records, Zhuang population derived from one of BaiYue ethnic group 2,000 years ago,the Luo Yue and Ou Yue. Recently,it seems to be commonly accepted that Zhuang population are descendants of these two branch of Bai Yue. Hainan Island is a big island in the Tonkin Bay between East Asia and Southeast Asia. Li People are the original inhabitants of Hainan. They are also believed to be the descendants of the ancient Baiyue tribes of China. The origin and migration of Li population are still on hot debates.In the present study, we dissected the genetic relationship between two populations--Zhuang and Li.To explor the maternal genetic relationships between Zhuang and Li population, analyzing mtDNA control region sequence, in order to trace the origin of Li and Zhuang population and provide genetic basis of migration in the history of the world.Materials and MethodsSamplesBlood samples were randomly collected from 888 healthy individuals, including 277 Zhuang residing in Guangxi Autonomous Region and 198 Li from Hainan Province. The 222 Han residing in Guangxi and 191 Han in Hainan region were used this study for comparison.All subjects are unrelated and confirmed for their genealogical information at least two previous generations. All individuals were able to confirm that the birthplace of their maternal grandmothers was in the same province.MethodGenomic DNA was extracted by using the standard phenol-chloroform method. After the mtDNA D-loop region was amplified, we sequenced the control region and the sequences were aligned against the revised Cambridge standard sequence (rCRS) using DNASTAR software.Combined with the coding region of the restriction fragment length polymorphism, we classified the mtDNAs motifs into the specific haplogroups. After all subjects were assigned into the right haplogroup respectively, the haplogroup distribution frequencies in each populations were computed. Median joining networks were carried out by NETWORK software to analysis the relationship of haplogroups. The principle component analysis was conducted by using SPSS 13.0 software package, Varimax-Rotation method was applied to our data.ResultsHaplogroup profiles To determine the genetic affinity between the Zhuang and Li populations, we typed mtDNA hypervariable segments from 888 individuals. We defined 90 different haplogroups, the predominant haplogroups in southern China:haplogroups B, F, and M7 together account for 64.3% and 69.7% of the populations Li and Zhuang, respectively.The frequencies of these common haplogroups reach to 37.5%. The haplogroup frequencies comparison of two populations shows that:The most frequent haplogroups are B4 (13.4%), B5 (10.1%), F (18.1%) and M7 (18.8%) for Zhuang in Guangxi, and B4 (20.7%), B5 (7.6%), F (20.2%) and M7 (20.2%) for Li in Hainan. Zhuang residing in Guangxi and Li from Hainan shared similar haplogroup frequency, no significant difference between the two samples.Principle component analysisWe input these data of populations haplogroup for the principle component analysis, involving the haplogroups data from Yunnan, Jiangxi, Hubei, Hebei and Henan. The PC map shows that the first two principal components could account for 84.629% of the total variation. It can be seen from the chart that the two populations from Guangxi and two populations from Hainan are close together. It showed that they not only geographically proximate but also have similar haplogroups. In contrast, the four populations (Henan, Hubei, Hunan, Jiangxi) are distant from each other in the PC map, although they are geographically proximate.Network analysisTo get more information about the relationships among Zhuang/Han in Guangxi and Li/Han in Hainan, we used hypervariable segments I (HVS-I) and II (HVS-II) motifs to construct median-joining networks here. The networks contain large nodes with primary, secondary,and further branching representing shared haplogroups among four populations. The networks show greater similarity in haplogroups among Zhuang/Han in Guangxi and Li/Han in Hainan. For example, the M7b haplogroup recognized by mutation 16297 and 150, which contains 10 Zhuang/13 Han in Guangxi and 6 Li/7 Han in Hainan. The Fla haplogroup remain approximately specific to four population. Although the branch, which is to say, Zhuang and Li population sharing the common haplogroups. Time estimateWe conducted age estimates of the several relatively high-frequency branches in specific haplogroups of Zhuang/Han in Guangxi and Li/Han in Hainan populations. M8 is a very old haplogroup, while B,R9,N9,F and M12'G haplogroups are relatively younger that each one about 50,000 years old. Some haplogroups, such as M7 and D, branches off about 40,000 years old.DiscussionThe mitochondrial DNA structure of the Hainan population is similar to Guangxi population. The matrilineal gene pools of both Zhuang and Li show more southen China genetic features. The dominant haplogroups of southen Chinese, B, M7 and F make up a proportion of 64.3% in the Zhuang population and 69.7% in the Li population, respectively. Because this pattern is consistent with the previous work on Y chromosome. it is highly likely that two populations originating from a common ancestral population.According to our results, the age of haplogroup M7 likely to be 40,000 years old, it is no significant difference among the Zhuang/Han in Guangxi and Li/Han in Hainan populations. The age would be considered as the gene flow for the peopling of southen China. However, the age of haplogroup M12 might be estimated the divergence time of Li populations.Meanwhile, the median-joining network was constructed with haplogroup M12 showed that the position of Li populations mainly located as a branch of the tree.This pattern reflected the history of population differentiation. It suggested that Li populations might be derived from Zhuang populations.The characteristics of haplogroup B4 and B5 present the star-like phylogeny in the network, which is very homogeneous in the four ethnic groups. The B4b lineages were concentrated in the Li people of Hainan, likely involving a founder effect. This clade is frequent in southern China where a match for the dominant B4 haplotype is also observed in our results. Haplogroup Flal, the branch of Haplogroup F, has been occured at high frequency in southen China.In Li populations, a high frequency of haplogroup F1al was observed specifically among the four southern populations. The coalescence time of haplogroup F in Li populations is 51.9±19.9 thousand yeas, and we observeed the clade in Zhuang populations has a coalescence time of 53.2±18.9 thousand yeas. The pattern most likely suggested that migration waves of ancestors of the current Li people were not rapid processes. Their gene pool could also be shaped by the subsequently demographic events in the process of migration and/or colonization.