Author: SL Lee
Date: 02-04-06 23:47
To characterize the mitochondrial DNA (mtDNA) variation in Han Chinese from several provinces of China, we have sequenced the two hypervariable segments of the control region and the segment spanning nucleotide positions 10171–10659 of the coding region, and we have identified a number of specific coding-region mutations by direct sequencing or restriction-fragment–length–polymorphism tests. This allows us to define new haplogroups (clades of the mtDNA phylogeny) and to dissect the Han mtDNA pool on a phylogenetic basis, which is a prerequisite for any fine-grained phylogeographic analysis, the interpretation of ancient mtDNA, or future complete mtDNA sequencing efforts. Some of the haplogroups under study differ considerably in frequencies across different provinces. The southernmost provinces show more pronounced contrasts in their regional Han mtDNA pools than the central and northern provinces. These and other features of the geographical distribution of the mtDNA haplogroups observed in the Han Chinese make an initial Paleolithic colonization from south to north plausible but would suggest subsequent migration events in China that mainly proceeded from north to south and east to west. Lumping together all regional Han mtDNA pools into one fictive general mtDNA pool or choosing one or two regional Han populations to represent all Han Chinese is inappropriate for prehistoric considerations as well as for forensic purposes or medical disease studies.
Intriguingly, despite the numerous historically recorded migrations and substantial gene flow across China from the Bronze Age to the present time (Ge et al. 1997), differences between geographic regions have been maintained. The regional difference is more pronounced in south and southwest China: in the PC map, the southern and southwestern populations show a more diverse pattern than the populations from central, east, and northeast China. The Zhanjiang and Guangzhou samples, though from the same province (Guangdong), differ considerably in their mtDNA haplogroup distribution. It thus seems that the Neolithic expansions from the Yellow River basin and later from the Yangtze River basin to other parts of China, as well as Bronze Age movements, did not erase local populations. The subsequent conquest of the Han in historical time, starting from central China, constituted mainly a political expansion process that led to the cultural assimilation of numerous ethnic groups under the dominant Han culture (Ge et al. 1997).
In summary, our phylogenetic analysis of 263 Han mtDNAs shows that ∼94% of the lineages can be allocated to specific subhaplogroups of the Eurasian founder haplogroups M, N, and R (which is itself a subhaplogroup of N shared between Europe and East Asia). Most of the nested haplogroups that are not infrequent have ages >30,000 years. It is conspicuous that the potentially most ancient of these haplogroups, R9 and B, may have their earliest diversification in southern China and/or Southeast Asia. A few possibly basal branches of M, present in Guangdong but absent or rare in northern China, still await a full description with more data from Southeast Asia. Only a restricted number of major subhaplogroups of M and N—namely, G, M8, M9, A, and N9—may be of central or northern Chinese provenance. All this makes an initial pioneer colonization of China ∼60,000 years ago from Southeast Asia conceivable (as proposed by Su et al. 1999; Jin and Su 2000) but still leaves much room for speculation about the population dynamics during the long period between then and the Last Glacial Maximum. The contrast between the northern and southern genetic pools might have its roots in this period. Subsequent migration events may have somewhat blurred this early distinction, with the genetic pools of central China possessing mtDNA features of both the northern and the southern pools.