Printed below is an excerpt from an article I came across recently. It is rather simple, if not elementary, but oftentimes that’s the best type of article to post on a blog that deals with complex, scientific concepts such as genetic genealogy. The article was written by Diahan Southard and appeared in the August 24, 2018 online issue of “familytree”. I encourage you to follow the link below and read the entire article. JT
If you take a DNA test, you can find out who your great-great grandparents were?
An autosomal DNA test can help you identify genetic cousins, but it can’t tell you exactly how you are related to those cousins. Your DNA testing company will provide an estimate of your relationship, indicating that you are 3rd cousins, or perhaps even more vaguely, 3rd to 5th cousins. It is left up to you to figure out how. This is no small feat. For example, you and a third cousin should share a common set of 2X great grandparents. You have 8 sets of 2X great grandparents, meaning that you have to figure out which one of the 8 sets is the one connecting you. How do you accomplish this? Well, you do genealogy! If another descendant of your great-great grandparents has been tested, and this DNA match has a paper trail, they might indeed be able to help you connect to them.
You could also use Y-DNA to help you in your search. However, one limitation of Y-DNA is that even with a perfect match in most cases you can’t determine whether you’re related through your 2X great grandfather or a more distant ancestor, unless you can find the records to prove your hypothesis.
Likewise, you could employ mtDNA to help, but you would have to be very targeted. For example, if you know that Janice is a documented direct maternal descendant of the 2X great grandparent couple that you believe to be descendent from, and you believe you too are their direct maternal descendant, then you could compare Janice’s mtDNA to your own. If you match, there is a good chance that you are on the right track.
The answer then, is yes, DNA testing can be a great tool to help you find your 2X great grandparents, but it will also take a significant amount of good ol’ fashioned genealogy research.
[Blog Editor’s notes: When you test with AncestryDNA, you are using an Autosomal DNA test (sometimes written as atDNA or auDNA). On the other hand, FamilyTreeDNA.com (FTDNA.com) offers a variety of tests including Autosomal DNA, Y-DNA (at three different levels), mtDNA, and several different combinations of these plus several advanced tests.]