My husband, T, had his autosomal DNA tested last May in hopes of finding out his heritage. This is a popular endeavor in the U.S. right now and at least one other blogger has written about it recently.
Autosomal DNA gives you information about all your ancestors, not just ones in a male or female line. When you get the results it also gives you biological matches to near and distant relatives who have also had their DNA tested on ancestry.com, telling you what the matches are to you, like siblings, 1st, 2nd, 3rd, and 4th cousins. Well, when he got his results it revealed to him that he has another biological daughter. BIG surprise! He had no idea. It was the 1960s, for crying out loud.
R was given up for adoption by her birth mother. She did her DNA test as a way to find her birth parents. Many of her DNA "cousin" matches had the same last name as T. Since she didn't know about T, and he had not yet submitted his DNA, the repeat appearances of those family surnames did not help her in her search. R assumed that she would not find her actual biological parents unless they submitted a DNA test via ancestry.com. Which is what happened with T.
She is a lovely person, solid and good. There are many interesting similarities between her (and her children) and the rest of T's family. We have grown-up grandchildren now, and another son-in-law!!!! Plus our daughter, M, now has a sister! When I wrote my bit about the concept of Grace a while back, this is what I was referring to; this unbelievably mind-altering, joyous cosmic gift.