> I'm pretty sure you would find that Han Chinese are less heterozygotic than other neighbouring Asian populations.

Yes, but that's less a function of openness to immigration than the enormous number of native Chinese. The development of rice farming lead to a massive demographic expansion in a very short period of time. It's mostly founder effects.

> Take for example, their Southern neighbour, India, I predict you see far more genetic variation.

You will, but that's more because the Indian population structure is I think, about 2,000 years younger. China's population has more or less one base. Modern Indians (subcontinent, not Republic) are a mix of Ancestral North Indian and Ancestral South Indian.

http://www.unz.com/gnxp/indians-as-hybrids-a-k-a-aryan-invas...