We promised to keep this series as science-free as possible, and instead focus on the practical use of AncestryDNA tests to identify your ancestors. We’re going to keep that promise here, but we want to say a few words about other types of DNA tests you can’t get from Ancestry, and how xDNA, yDNA, and mtDNA can be useful! Just remember, we’re generalizing a bit here, and if you want the detailed science behind all of this, Google has many great reads.
yDNA and mtDNA
yDNA and mtDNA come only from your father and your mother, respectively, and change very little over the generations. These tests are often written off in the genealogical community, because they won’t, by themselves, lead you to how you are matched with someone, or how many generations back you might match them.
For example, if our Michael has a yDNA test and he matches “Frank” who shares the same yDNA…it tells us next to nothing. From the test we know that on Michael’s paternal line we have proved he’s matched to Frank…but there’s no way to tell how. It could be 1000 years ago we all had a MRCA, or it could be that Frank’s 4xGGF was a brother to ours, but there’s no way that kind of range will narrow it down by itself.
There are two uses of yDNA and mtDNA, however, that makes these some of the most powerful tests you can take:
Unlike “ethnicity” estimates we see from all the major testers, yDNA and mtDNA can be very effective in pinpointing very accurately the location of your ancestors on the planet. The standard (Autosomal) DNA tests from Ancestry rely on a small global sample of historical DNA (16,000 samples currently), and human created Family Trees, to mathematically try and guess where our ancestors were 800-1000 years ago. They are looking for little shreds of DNA to trace back, and it’s very small amounts because Autosomal DNA gets cut in 1/2 for each side of a lin ever generation. However y/mtDNA doesn’t change over the generations and so we know very accurately where those ancestors were, based on where the bodies were found. This is especially important for African American genealogy, when there are nearly no records of origin before our ancestors were taken from Africa. These tests can be very accurate, and place your ancestral group in to very small physical and/or social (tribal) locations.
Brick wall research
In our example above, we know for a scientific fact that Michael and Frank share an MCRA along their paternal line. The same is true for women who have an mtDNA match. While that again doesn’t help us much if we have no information, it’s invaluable if we have a good guess on how we’re related. Let’s go back to our DNA Painter walkthrough to see how we wish we had yDNA and mtDNA tests.
To recap from last week’s post, we have two lines of DNA tests that we know are connected, and we have narrowed down the MCRA for both a cluster of AncestryDNA matches and on our line, but we don’t know how they connect. So, we have two couples (Jacob/Maria Kupsch, and Joseph/Dorothy Haasl) that we know match, most likely 2-3 generations above them. Each of them have 8 potential match relatives, and we have 4 known relatives, so we’re facing 32 ancestors that might be our MCRA.
But, if we can confirm the y/mtDNA from those 4 relatives, whom all died over 100 years ago, because that DNA doesn’t change between generations. That means a direct male relative from Jacob (say his son’s, son’s, son’s, son’s DNA) will confirm Jacob’s yDNA. Same for Maria, and a direct female relative. If we could yDNA test relatives of both Jacob and Joseph, and mtDNA for both Maria and Dorothy we would have about a 25% chance of finding an immediate match. And, if say Maria and Dorothy share the same mtDNA we just figured out we need to focus our research only on both of their maternal lines to make our match. If we don’t find that match, we just eliminated 25% of our potential match points, so now instead of building out 32 ancestors to find our match, we’re down to 24. But even better, if we can go one level up and do the same thing, we can eventually narrow this down to where we share an MCRA.
Here’s a great blog post that breaks this down a real-world example from Roberta Estes: (Mitochondrial DNA Bulldozes Brick Wall)
Going back to the GEDmatch installment of this series (How to make the most of your AncestryDNA matches: Part 4 – How to quickly, and effectively, use GEDmatch), there was a column in our DNA matches that showed the amount of xDNA that we matched other testers. The good news is that all of the major test kits include xDNA measurements in their most basic test. The bad news is, it’s unlike the other types we’ve talked about, and it’s almost useless. With one very valuable exception.
It would be highly unlikely we could ever build out a family match with xDNA, and the cM you share with someone tells you almost nothing about close of a match you are with them. The main value of xDNA is if you do match someone, it narrows down your link to that match in a very powerful way. xDNA is inherited in a unique pattern that going back several generations can eliminate more than 50% of your tree as a potential match.
Women will inherit an X chromosome from both their mother and their father, but men will inherit an X from only their mother. Going back to High School Biology, we quickly remembered that women have an XX chromosome, while men have XY!
But, the value for us comes in when we build out our potential ancestor’s chart, using that inheritance pattern. So, if we have a female test subject who has an unknown xDNA match, we know it’s not from her Father’s Father’s line because men only inherit their X from their mothers. Going back 2 generations, we just eliminated 25% of the potential matches. If you know, from other research, that this unknown match is on their father’s line, you just confirmed it’s on the father’s mother’s line.
You won’t see a lot of xDNA matches, but when you do, Google one of the many xDNA inheritance fan charts, and start to see if you can eliminate suspects in how you match. It could bring you much closer to where to hunt for your MCRA.
Here’s a great break down of xDNA from DNA Explained, with more links to more detail as well: (Who Tests the X Chromosomes)
Just know that all of this work will have to be in GEDmatch however, since AncestryDNA doesn’t provide any information on the details of your genetic matches, and none of the tools needed to view/manage this information.