I got to thinking, could they really prove by DNA that Sophie was a descendant of Mary Magdalane?
If the two of them lived about 2000 years apart, that's approximately 100 generations. A parent passes half of their DNA onto their child. The amount of genetic material that a grandparent contributes is affected somewhat by random chance, but is approximately one fourth. So two to the hundredth power is 1,267,650,600,228,229,401,496,703,205,37
Basically what I'm saying is that if you go back more than a few generations, ancestry really starts blending together and from a genetic standpoint it doesn't really matter from whom we're descended.
The only way for that bloodline to stay pure would be for that family to only mate with itself for 2000 years... eek.