Why test yDNA only?? 1. Because a female receives one X chromosome from each parent. So testing DNA from X chromosome (of a female subject) could not reveal from which parent the DNA had been received. You'd have to test at least one of her parents, too. 2. Testing DNA from X chromosome of a male subject, of course, would show DNA material which he could only have received from his mother. He can prove who his mother was. But that's as far back as can be ascertained, because DNA from his mother could have come from the X chromosome she received from her mother, OR from the X chromosome she received from her father (see part 1). Therefore it would not be possible to tell from which of his mother's parents the grandson's xDNA had been received. So if we text xDNA, we would have to backtrack through records of xDNA results from every generation, which wouldn't get us back very far in time. Maybe at some point in the future, if a database of xDNA matched to names existed, it would be possible to prove a lineage through testing xDNA. It would still be a lot more work to do it that way, though. Hope this helps. Liz J