Principal component analysis of gene frequencies of Chinese populations

Principal components (PCs) were calculated based on gene frequencies of 130 alleles at 38 loci in Chinese populations, and geographic PC maps were con structed. The first PC map of the Han shows the genetic difference between Southern and Northern Mongoloids, while the second PC indicates the gene fl ow between Caucasoid and Mongoloids. The first PC map of the Chinese ethnic minorities is similar to that of the second PC map of the Han, while their second PC map is similar to the first PC map of the Han. When calculating PC with the gene frequency data from both the Han and ethnic minorities, th e first and second PC maps most resemble those of the ethnic minorities alo ne. The third and fourth PC maps of Chinese populations may reflect histori cal events that allowed the expansion of the populations in the highly civi lized regions. A clear-cut boundary between Southern and Northern Mongoloid s in the synthetic map of the Chinese populations was observed in the zone of the Yangtze River. We suggest that the ancestors of Southern and Norther n Mongoloids had already separated before reaching Asia. The ancestors of t he Southern Mongoloids may result from the initial expansion from Africa or the Middle East, via the south coast of Asia, toward Southeast Asia, and u ltimately South China. Upon reaching the Yangtze River, they might even hav e crossed the river to occupy the nearby regions for a period of time. The ancestors of the Northern Mongoloids probably expanded from Africa via the Northern Pamirs, first went eastward, then towards the south to reach the Y angtze River. The expansion of the Northern Mongoloids toward the south of the Yangtze River happened only in the last 2 or 3 thousand years.