* Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, Yunnan, China
Graduate School of the Chinese Academy of Sciences, Beijing, China
Taishan Medical College, Taian, Shandong, China
Fachbereich Mathematik, Universität Hamburg, Hamburg, Germany
|| Yunnan University, Kunming, China
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Abstract |
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Key Words: mtDNA ancient DNA Han Chinese
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Introduction |
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A dissection of mtDNAs into major (and minor) haplogroups is essential for identifying spatial frequency patterns (Torroni et al. 2000, 2001). Thus, there are two prerequisites necessary for an interpretation of relatively short fragments of ancient mtDNA from East Asia: (1) a reliable basal phylogeny of the major East Asian mtDNA lineages based on control region and coding region information (Kivisild et al. 2002); and (2) a large database of modern East Asian mtDNA HVS-I (and HVS-II) sequences linked with partial coding region sequences, or at least single haplogroup-diagnostic sites screened by restriction fragment length polymorphism (RFLP) typing (Yao et al. 2002a). With this information at hand, one can often infer the potential haplogroup status from a short segment of the control region (which is typical for ancient DNAs) through a haplogroup-specific HVS-I motif search and matching or near-matching with the mtDNA haplotypes in the database (Yao et al. 2002a).
Until now, only two modern mtDNA samples (Zibo, with 185-bp fragments of HVS-I [Wang et al. 2000], and Qingdao, with HVS-I and HVS-II sequences and additional coding region information [Yao et al. 2002a]) from Han populations of Shandong have been analyzed for mtDNA variation. In the present study, we sequenced the mtDNA control region in 76 Han individuals from Taian, Shandong, and combined these data with the reported Zibo and Qingdao samples in order to elucidate the (matrilineal) genetic structures of contemporary populations from Shandong. Then, by contrasting the frequency distributions of the mtDNA haplogroups tentatively identified in the ancient DNAs with the modern data from Shandong as well as from other provinces of China (Oota et al. 2002; Yao et al. 2002a, 2002b; Yao and Zhang 2002 and references therein), we reassessed the conclusion of Wang et al. (2000).
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Materials and Methods |
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Haplogroup Assignment
We adopted the mtDNA haplogroup classification tree and nomenclature system described in recent studies (Kivisild et al. 2002; Yao et al. 2002a) for mtDNA assignment. The haplogroup status of the 2,000-year-old (Oota et al. 1999) and 2,500-year-old (Wang et al. 2000) mtDNAs was tentatively inferred according to the strategy described in the Introduction and in recent studies (Kivisild et al. 2002; Yao et al. 2002a; Yao and Zhang 2002). Some ancient mtDNAs that could not be classified unambiguously were left unassigned and were marked as "?" for haplogroup status. The frequency vectors of mtDNA basal haplogroups (M7, M8, M9, M10, M*/N*, G2, D, A, N9, B, R9, and R* [Yao et al. 2002a]) in 16 regional Han samples across China (Kivisild et al. 2002; Oota et al. 2002; Yao et al. 2002a and references therein; this study) and the two ancient samples were subjected to principal component (PC) analysis.
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Results and Discussion |
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The mtDNA haplogroups that could be positively identified (albeit at different levels of certainty) in the two ancient populations are "Asian-specific" (see table 1). Moreover, some of the haplotypes in the ancient DNAs match exactly those from modern samples. For example, types M7b2 (16223-16297-16298), M* (16223-16311), M* (16223), A (16223-16290-16319-16362), D5a (16223-16266-16362-150-263), and C (16223-16298-16327) in the ancient mtDNAs could be matched to haplotypes observed in the three modern samples from Shandong. The F1b type (16232A-16249-16304-16311-16344) in the 2,500-year-old population matches a haplotype observed in Han people from Yunnan Province, and the motif 16232A-16249-16304 is widespread, found in individuals from Xinjiang, Yunnan, Liaoning (Yao et al. 2002a), Shaanxi (Oota et al. 2002), and Shandong (this study). The specific motif (16291-16304) of F2 types in the 2,000-year-old populations are also found in contemporary Han individuals from those provinces as well as individuals from some ethnic groups in Yunnan (Yao et al. 2002b). It is therefore far from conclusive that "the 2,500-year-old population showed greater genetic similarity to present-day European populations than to present-day East Asian populations, and the 2,000-year-old population had features that were intermediate between the present-day European populations and the present-day East Asian populations" (Wang et al. 2000, p. 1396).
Figure 1 gives a PC analysis view of the 16 regional Han samples across China and the two ancient samples based on the frequency profiles of the basal haplogroups (Yao et al. 2002a), whereby the unassigned types marked as "?" for haplogroup status were disregarded (a tentative scoring as R* would only emphasize potential outlier status [data not shown]). The 2,500-year-old and especially the 2,000-year-old samples show closer affinity to the modern samples from the south than from the north, thus reflecting the trend in the haplogroup profiles discussed above: haplogroups F and B have higher frequencies in populations from the south (or of southern origin) than those from the north (or of northern origin) (Yao et al. 2002a).
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In short, both the 2,500-year-old and the 2,000-year-old Linzi populations had features in common with the modern populations from south China rather than any specific affinity to the European mtDNA pool. The following scenario could explain the changes in the matrilineal genetic structure of the Shandong populations during the past 3,000 years: before or during the Spring-Autumn and Warring States era (770 B.C. to 221 B.C.), migrations from south and central China could have heavily contributed to the gene pool of Linzi inhabitants, as Linzi was the capital of the feudal state of Qi, which was famous for its economy and development at that time (Ge, Wu, and Chao 1997). Later, the conquest by the Han coming from central and north China in historical time and the occasional invasion of northern nomadic tribes to this region might have brought major shifts in the composition of the resident population (Ge, Wu, and Chao 1997), which eventually led to the genetic pattern we observe today. To reconstruct the evolutionary history of China, it is thus important to take (pre)historic knowledge and archaeological assemblages into full consideration. Our results highlight that the interpretation of ancient DNA should begin with sufficient data and not draw conclusions on too limited a data set. Molecular anthropology would profit from embracing the research done in medical genetics and forensics: both are employing or are beginning to use coding region information (Herrnstadt et al. 2002; Lee, Lee, and Lee 2002; Kivisild et al. 2002 and references therein). For unambiguous conclusions, it is indispensable to include coding region polymorphisms that are diagnostic for mtDNA haplogroup membership in addition to sequencing portions of the HVS-I when trying to establish the geographic/genetic affinities of ancient samples.
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Acknowledgements |
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Footnotes |
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Jeffrey Long, Associate Editor
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Literature Cited |
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