DNA Musings No. 15: Using DNA to confirm your family tree

The challenge
Look through your family tree and identify each direct ancestor for whom you have evidence that he or she is biologically related to you.

How to proceed?
One way to approach this is to confirm a DNA match descended from a sibling of your direct ancestor and verify that the amount of DNA you share is consistent with the documented relationship. This is evidence that your ancestor is genetically related to you.

For example, how do I know that I am really the biological grandchild of Emma Peterson? Emma’s sister Lyda had a son Lloyd. He is my Mom’s first cousin. Lloyd had a daughter Cheryl and she is my second cousin. Cheryl took a DNA test and she and I share 315 cM. The Shared cM Project shows that the average shared DNA for second cousins is 229 cM with a range of 41 to 592. Our shared DNA is within the expected range. Cheryl’s grandmother and my grandmother are sisters on paper and the DNA supports that. This, then, is evidence that I am biologically related to my Grandmother Emma. And by extension, to at least one of her parents. Is it proof? No. Just another piece of evidence.

More evidence leads to a more accurate tree.