According to my family history I am of northern Chinese descent. DNA analysis indicated that it might have to go a bit further north, across the Great Wall. Specifically, since my paternal haplogroup is C3*, it is closer to the Mongols than the Manchus (whose emperors carried C3c, a related but different thread). There is also a non-trivial chance that my Y-chromosome came from Genghis Khan, who has left a wide genetic footprint across the former Mongol empire.
To clarify, the paternal haplogroup only traces the Y-chromosome, not the entire ethnic composition. I am pretty sure it is not uncommon for northern Chinese to have some Mongolic blend.
Furthermore, my maternal haplogroup is D4e3 (likely coastal Chinese). So I am probably some combination of Mongolian and Han Chinese.
My grandfather once told me that our last name came from one of the seven warring states. Clearly, he thought we were (pure) Han Chinese. I am having fun imaging his reaction upon hearing his true ancestry.
I plan to use this to explain away my past and future behaviors.