To better illustrate why the Ancestry DNA shared ancestor hints should be used only as a suggestion of where the possible connection may be with your DNA match, rather than something taken at face value as confirmation of where the connection is with your DNA match, I wanted to create an example to show how a shared ancestor hint can be completely wrong and misleading. As you can see, in the list of matches for my maternal grandmother’s brother (R E H), he has a shared ancestor hint with both myself and my mother, as indicated by the leaf next to the number of people in our respective trees.
Upon clicking on my name to look at the details of the match with me, it shows the shared ancestor hint, and the specifics of how we are related. It is showing we share John Q. Sample as our most recent common ancestor.
Looking at the details of John Q. Sample, you can see how I purposely used dates which are impossible, in addition to the completely fabricated name.
How did I get this result? I first removed my great grandparents as the parents of my maternal grandmother and my maternal grandmother’s brother (R E H). Next, I created my fictitious John Q. Sample, and then attached him as the father of my grandmother and her brother. I waited a few hours to allow the Ancestry DNA system to process the change, and the shared ancestor hint then appeared. This would be the same result as if someone had attached an incorrect person to their Ancestry member tree and taken an Ancestry DNA test. If your DNA happens to match the test taker, and the incorrect person they have attached to their tree as one of their direct ancestors happens to match one of your direct ancestors in your tree, a shared ancestor hint will be shown in each of your match lists.
As I hope this example clearly shows, the shared ancestor hint is only indicating that you and the other person have the same person in each of your trees as a direct ancestor. It is not an indication of the accuracy of the person’s tree, nor is it in any way a verification of where in your tree the DNA connection is. The only way you can properly verify the accuracy of the match, and with which ancestor(s) the match exists, is to use a chromosome browser (such as the one at the GEDmatch site) to make sure the same chromosome segments are shared by at least three people who share the same direct ancestor(s). This is called triangulation. How to go about doing triangulation will be the subject of my upcoming posts on how to use the GEDmatch site and tools.
For those who reached this post from the example link, return to Chromosome Mapping And GEDmatch: An Overview Of What They Are And What The Benefits Are.
This article last updated 16 Dec 2014