I understood the little video with the family tree and the XY chromosome business, but then they lost me completely with the next video (of the male prof reading from his notes)

Also, perhaps I missed it in the science "stuff" that flew way over my head, but no mention of using the X chromosome to trace ancestors? So, why did Chris' brother do the DNA test not her? See, I'm definitely not getting this DNA malarkey, am I?

STG