In a message dated 6/1/2010 8:17:23 A.M. Eastern Daylight Time, [email protected] writes: >> I have a question for you about using DNA testing to prove relationships. I have spent years trying to prove who my maternal grandfather's father was. I found a man that I suspect was his father and need to prove it. This man never married my grandfather's mother (not unusual I guess), but he later married two other women. One of whom had a son with him. This son had two daughters who are still living, as is my mother (age 96). Can I use DNA testing, such as "23andMe" to prove that they are related? << Hello Pat! Here's another non-Linda response! First, let me emphasize that I agree with everything in Joan Young's post. She hits several nails squarely on their heads. Let me add however that if I understand your message correctly, your mother is hypothesized to be a 1/2 first cousin of the two additional women in question. Now, the "theoretical" amount of DNA one shares with a 1/2 first cousin is 6.25%. But in the "real world" the actual percentage could be as much as a point or two higher or lower. Therefore, if you should purchase an autosomal DNA test for your mother plus the same test for at least one of the two other women -- either a test from 23andMe, or from FTDNA, per their new Family Finder offering, I'd say any matching percentage from four to eight could legitimately be seen as confirming the hypothesized relationship. Such an outcome wouldn't constitute absolute, metaphysical "proof," but I suspect it would be good enough for us to take to the bank. Three additional thoughts: 1. By all means try to obtain a DNA sample from your mother. FTDNA will store it indefinitely, and 23andMe will store it for ten years. That way, even if the two other women don't test right away, you'll still have the option of comparing to your mother if they relent after a while. Also, the science of molecular biology advances so rapidly that completely new testing options will probably come on stream over the next five to ten years. 2. Although a DNA sample from only one of the two other women would probably be sufficient to test your theory, it would be much better to have samples from both. That's because the random nature of DNA recombination means they might match your mother at different chromosome locations. And by identifying these differing locations, you MIGHT have info that eventually would help you analyze DNA matches between your mother and other people as yet unknown. 3. In terms of raw cost, FTDNA's test is the better deal. Also, it almost surely will have more genealogical potential over the long run, when the FTDNA data bank eventually outpaces that of 23andMe -- not to mention the fact that every FTDNA test is for genealogy alone, whereas most 23andMe testers are looking for health info. On the other hand, 23andMe has the clear short-run advantage of a much larger customer base among which to seek matches, plus 23andMe offers a veritable "mountain" of health-related info you won't get from FTDNA. So depending on your personal circumstances and goals, either company could be entirely satisfactory for your purposes. Best regards, Jim Brown (James Armistead Brown, Jr.) Administrator, Brown DNA Study Administrator, Knox DNA Project