Plot logic flaw?

Rating: 5/10 (19 May 2006)

I can overlook the historical inaccuracies that plague the movie. Without them there would be no conspiracy theory to drive the plot along. However, I must have missed something by not reading the book. The premise that seems to drive the plot is essentially "if we can actually find Mary Magdalene's body we'll be able to look at the DNA and prove that Jesus has descendants who walk the earth today. That'll shake up the power structure of the oppressive church and people will be free!!!"
But my problem came toward the end. The movie seems to rely on the fact that DNA analysis will be the key to finding the royal line of Jesus that's currently walking the earth. I'll overlook the fact that it's highly unlikely that anyone could prove conclusively that they've actually FOUND Mary Magdalene's body. I was willing to concede on that point because of the great ride of twists and turns and betrayals and layers of meaning that the movie had woven up to that point. But here's my problem: How can DNA analysis on Mary Magdalene alone prove that the person is a descendant of Jesus? Wouldn't they have to have Jesus' DNA to prove that? I'll have to watch the movie again. Maybe I missed something. I guess that's what spoiled the movie for me. The climax of the film was built on faulty logic.