AncestryDNA Matching Update Impacts Jewish Ancestry
Ken Chahine, Ph.D., J.D.
AncestryDNA customers with significant Jewish ancestry have witnessed the challenges that we and other genetic genealogy testing companies have faced when predicting genetic relatives. Most Jewish customers find that we predict them to be related to nearly every other Jewish customer in the database! So while we all know that the cousin matches for Jewish and some Hispanic customers were over-estimates, detecting which cousin matches were real and which ones were bogus has always been a challenge for these populations.
The AncestryDNA science team has been unsatisfied with the cousin matches we have delivered to many of our customers and as part of our continued commitment to bring innovative genomics to you, we are pleased and proud to tell you that we have found the first solution to the “overmatching” experienced by Jewish, Hispanic and other customers.
When you take a step back, matching isn’t as simple as it might first appear. After all, we are all 99% identical. In other words, determining which parts of our genome make us “human” and which make us “recent cousins” is tricky and at the heart of the cousin matching issues for customers of Jewish and Hispanic ancestry.
In DNA matching, we are looking for pieces of DNA that appear identical between individuals. But there are a couple of reasons why it could be identical. For genealogy research we’re interested in DNA that’s identical because we’re both descended from a recent common ancestor. We call this identical by descent (IBD). This is what helps us to make new discoveries in finding new relatives, new ancestors, and collaborating on our research. However, we also find pieces of DNA that are identical for another reason. At one extreme we find pieces of DNA that are identical because it is essential for human survival. At the other, we find pieces of DNA that are identical because two people are of the same ethnicity. We call these segments identical by state (IBS) because the piece of DNA is identical for a reason other than a recent common ancestor. This, we have found, often happens in individuals of Jewish descent. Given the historically small population size of the Jewish community, two Jewish individuals might have a lot of DNA that looks to be identical. But that identical DNA might only be because of their shared ethnic history – in other words, identical by state, not identical by descent.
The challenge in DNA matching is to tease apart which segments are IBD, and which ones are IBS. How did we do it? By studying patterns of matches across our more than half a million AncestryDNA customers, we found that in certain places of the genome, thousands of people were being estimated to share DNA with one another. This isn’t a hallmark of thousands of people actually being closely related to one another. Instead, it’s likely a hallmark of a common ethnicity. Our scientific advancements using such insights from more than half a million people have allowed us to effectively “pan for gold” in our matches – by throwing out matches that appear to only be IBS, and keeping those that are IBD.
What does this mean for you?
While the problem was more pronounced in customers of Jewish and some Hispanic descents, we observed this problem across all ethnic groups. So, all customers will see increased accuracy of their DNA matches, and significantly fewer “false” matches.
Eager to see your new set of DNA matches? It will be available in the coming months, and we’re planning to email our existing AncestryDNA customers when the new matching results are ready with more information about what to expect and what it means for your research. So when the time comes, we’re excited to hear about the new family history discoveries you’ve made or distant cousins you connected with through the advancements of our updated matching service. I’m expecting a lot of great stories will surface, and we can’t wait to hear yours.