I just watched The DaVinci Code with my parents... I haven't read the book but it was a good movie. Total ripoff of Dogma though ;)
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 1,267,650,600,228,229,401,496,703,205,376. About one million trillion trillionth of Sophie's genome should be inherited from Mary Magdalane (assuming no inbreeding). I googled "human genotyping" and saw that the expensive fancy genotyping platforms currently screen about half a million SNPs (Single Nucleotide Polymorphisms, pronounced "snips"). So, no way. I was worried I'd have to do actual statistics to figure out the power of the test, but nope. In fact, the human genome is only around three billion base pairs long, so it is highly unlikely that Sophie has a single nucleotide from Mary Magdalane. Of course, there have never been a million trillion trillion people in the world, specifically not at the time of Christ. So in that sense we're all inbred, because we all have thousands or millions of people who lived two thousand years ago who each ended up as our ancestor many times over.
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.