How can I narrow down relationships in my DNA test results?
QFollowing a 40-year search for my father’s dad, which due to DNA is now close to a conclusion, I have a dilemma. My research suggests my dad’s father could be a 15-year-old (as was his mother). I have worked out two possible scenarios but the DNA match with the one relative I have established lies between the two expected values. Can anyone help?
Keith Burgess-Clements
It’s always exciting when DNA provides us with matches that can help us to break through brick walls, but unfortunately DNA on its own doesn’t provide us with all of the answers. In this example, we cannot determine from the DNA
Aalone whether the match is a second cousin or a half first cousin. There are probability tables on ancestry.co.uk that will give you the range of possible relationships. You can find this feature by clicking on the total centiMorgans (cM) shared. You can also check out the probabilities by using the Shared cM Tool on the DNA Painter website ( dnapainter.com/tools/sharedcmv4). This gives us a 49 per cent probability that the match is a half first cousin, and a 46 per cent chance that the match is a second cousin. I am assuming that all of the alternative relationships have already been eliminated.
However, it should be possible to work out which relationship is more likely by looking not at the match in isolation but trying to determine how the match fits in with the genetic network of shared matches. Check the list of ‘Shared Matches’ or ‘In Common With’ matches, and see if you can identify a common ancestral couple in the trees. If there are enough close matches and trees are available, you should find that the jigsaw pieces in the genetic network will only join together in one particular way. You could also try using DNA Painter’s What Are the Odds? tool ( dnapainter.com/tools), which will allow you to create a probability tree from multiple matches. If there are not enough close matches to solve the problem, you will need to identify and test putative cousins from the two possible trees. Debbie Kennett