23andMe made a significant change about the time I was recording my RootsTech presentation about triangulation which provided examples at each vendor. Unfortunately, there was no notification to customers, so most people still aren’t aware.
In the fall and winter of 2020, 23andMe made several changes that resulted in losses to the genealogy community.
At first glance, it looks like this particular change is cosmetic – simply a column heading title change – but there are modifications behind the scenes that negate triangulation at 23andMe. At least in the way triangulation previously worked with the functionality genealogists have long understood to be triangulation at 23andMe.
This article explains the changes, what they mean, and how to work around the issues.
Update
Please note that as of March 12, 2021, some of the changes seem to have reverted, but it’s unclear if all changes have reverted to the original status. It’s virtually impossible to confirm because testers cannot search for “Relatives in Common” by surname. Therefore, proceed by confirming that people who are marked as “Yes” for “DNA Overlap” do in fact triangulate on each overlapping segment using the techniques I’ve described below.
Triangulation
If you need a refresher about what triangulation means, how it works, and why it’s important, I’ve compiled triangulation resources into one article, Triangulation Resources in One Place.
Let’s look at what happened at 23andMe.
Before the Changes
Before the changes, it was possible to quickly determine if you triangulated with two other people on at least one segment by looking at the “Shared DNA” column. Now, it isn’t.
This change has HUGE ramifications.
Unfortunately, it’s easy to simply not notice the change or interpret the column heading change from “Shared DNA” to “DNA Overlap,” as unimportant, but that’s not at all the case.
A “Yes” in this column NO LONGER MEANS triangulation.
This change makes the 23andMe slides of my RootsTech session, DNA Triangulation: What, Why, and How, obsolete.
I’m rewriting that section, step by step, in this article.
Previous Information
Click any slide to enlarge
On slide 24 of my presentation, available here, I talked about clicking on a match, then scrolling down to the “Find Relatives in Common” link. If you click on that link, you see a list of who you and that match both match in common.
In this case, Everett Harold (not his surname) and I both match with my V4 kit, DH and Stacy.
That page, back then, had a column titled ‘Shared DNA.”
At that time, a “Yes” in “Shared DNA” meant that the three people triangulate on at least one segment. That’s not what it means now, and the column header has changed too.
What I said in the presentation was this:
“Looking under the Shared DNA column, the people with a Yes triangulate, and the people with a No, do not.
This means that Everett Harold, me, and DH triangulate. It also means that Everett Harold, Stacy, and I do NOT triangulate.”
Please ignore this and the next slide, #25, too, because the 23andMe page has changed – along with the meaning.
Just put what I said and what you think you know about how triangulation works at 23andMe out of your mind. If you haven’t yet watched my Triangulation session at RootsTech, please just simply skip those two slides (24 and 25) so you don’t confuse yourself with old and now irrelevant information.
We’re starting over here with triangulation at 23andMe.
Current 23andMe Information
Here’s the same 23andMe “Relatives in Common” page, today:
Click to enlarge
You can see that while Stacy was marked “No,” on the previous “Shared DNA” page, the column is now titled “DNA Overlap” and she is now marked “Yes.”
The new infographic says this:
Here’s what this change means:
- Previously, if someone was marked as “Yes,” it meant that in fact all three people did share a common segment of DNA AND matched each other on at least one segment. That meant they triangulated on at least one segment.
- Currently, this field only means that they share an overlapping piece of DNA with the tester. It DOES NOT mean that they all 3 match each other on that segment.
- They may or may not triangulate.
You might be wondering how that’s different. It’s very different and quite important.
Overlap Versus Triangulation
Here’s an example of two people who both match me on chromosome 15 and are marked “Yes” in DNA Overlap. Based on this graphic alone, or that “yes,” you can’t determine if this overlapping segment means triangulation, where the orange and purple person also match each other, or not.
- BOTH of these people match ME on chromosome 15.
- If they also match each other on a reasonable portion of chromosome 15 where they both match me, then we all triangulate. A reasonable amount of matching DNA at 23andMe is 6 cM, their match threshold.
- If those two people do not also match each other on a reasonably sized segment (6 cM) of chromosome 15, then we do not triangulate. This would indicate that one match is from my mother’s side, and one from my father’s side, or that perhaps one is identical by chance. In other words, we do not share a common ancestor on this segment which is the purpose of identifying triangulated segments.
Based on other comparisons which I’ll show you how to perform in a minute – the purple and orange people don’t match each other on this segment. Therefore, this segment is not triangulated between me and the purple and orange people.
Previously, for this match, the “Shared DNA” column was marked “No,” and now the “DNA Overlap” column is marked “Yes.”
The three of us don’t triangulate, and “DNA Overlap” now only means that the three people share some DNA on the same portion of a chromosome with me, NOT that they match each other, which would mean that we triangulate.
It’s a hugely important distinction.
Before, “Yes” meant triangulation and now “Yes” just means an overlap, but NOT necessarily triangulation. You have to figure that out for yourself.
Overlap at 23andMe
An overlap simply means that two people match you on the same portion of DNA.
Someone from your Mom’s side and someone else from your Dad’s side will both match you on a segment of DNA in the same location on a chromosome, shown above. However, they won’t match each other because one is from your Mom’s side and one is from your Dad’s side. Your Mom’s DNA is different from your Dad’s.
To prove that you all three share a common ancestor, you all three need to match each other on the SAME reasonably sized overlapping chromosome segment.
However, things are even more confusing now at 23and Me.
An Additional Complication
23andMe now indicates that Everett and Stacy have a DNA overlap with me, but the chromosome browser shows NO overlap on any chromosome when I compare both Everett and Stacy to me on my chromosome browser.
How is no overlap even possible when Stacy is listed on the Shared Relatives list with me and Everett, AND 23andMe shows a yes for DNA Overlap?
I eventually found the answer, which makes match analysis much more cumbersome for genealogists. What used to be one step now takes several, not to mention the “yes” answer is now unreliable.
Essentially, all that “Yes” in the DNA Overlap field means is a hint for you to dig further.
Determining 23andMe Triangulation
It appears that the only way to tell if your two matches match each other on the same chromosome as you is to “Select different relatives or friends to compare” at the top of the chromosome browser page.
You’ll see your name plus the two people you were comparing against your DNA in the chromosome browser.
You’ve already seen how they match you on the chromosome browser. What you now need to view is how they match each other.
You can remove yourself, and replace your name with one of your two matches, as shown below.
This will show Everett’s chromosome with Stacy compared to him.
Everett and Stacy do match each other on two smallish segments, but not in the same locations as shown on their match with me.
This is Everett’s match with Stacy (purple).
I match Everett on chromosome 18, but not Stacy.
I match Stacy on chromosome 7, but not Everett.
There is no overlap shown.
Ok, I’m adding myself to Everett’s matches, just to double-check.
Next, we’re looking at Everett’s chromosomes in grey. Stacy is purple and I’m orange.
Overlap Issue
I’ve found the confusing overlap issue, but it only makes the situation worse.
Everett matches both me and Stacy on adjacent and very slightly overlapping portions of chromosome 18. However, the amount of DNA where I match Stacy on chromosome 18 is too small to be considered a match when compared to Stacy directly, meaning it’s less than 6 cM – the smallest 23andMe segment to show as a match. This tiny sliver of overlap only shows when comparing from Everett’s perspective where we can see his match to me and Stacy both on the same chromosome.
A secondary change is that now it appears that 23andMe is showing any small piece of overlapping DNA with a “Yes.” Any segment of DNA smaller than 6 cM, their match threshold, should not be listed as overlapping if we all three don’t match each other on at least 6 cM of DNA.
You can work around the changes 23andMe made, but it has made a one or two-step easy process into a more complicated, cumbersome multi-step procedure involving comparing multiple people to each other separately.
Summary
| Previous | Now | |
| Column Title | Shared DNA | DNA Overlap |
| Triangulation Status | Triangulation if “Yes” in the “Shared DNA” column | Not an indication of triangulation, even if “Yes” in the “DNA Overlap” column |
| Triangulation Indicator | “Yes” in the “Shared DNA” column | None, triangulation not flagged |
In summary, for triangulation now at 23andMe:
- The DNA Overlap status of “yes” DOES NOT indicate triangulation.
- The DNA Overlap status of “yes” indicates overlap on the same chromosome, not triangulation, meaning all three people do not necessarily match each other.
- DNA Overlap status of “yes” MAY mean the three people triangulate, but further comparisons are needed.
- DNA Overlap status of “yes” may refer to overlap smaller than 6 shared cM which is not reflected in individual one-to-one matches.
- The DNA Overlap status of “yes” may therefore not be technically accurate in terms of genealogical matching and triangulation.
- A DNA Overlap status of “no” means you do not overlap which means you cannot triangulate.
- To determine triangulation, meaning if you and two other people all match each other if you share an overlapping segment of DNA on the same chromosome, compare each pair of people one-to-one in the chromosome browser.
- If you do not find overlapping DNA when comparing three people one-to-one, try the same comparison to the other two people from the perspective of one of the other people in the group, as I did with Everett. This may reveal a small overlapping segment, as illustrated in this article on chromosome 18 when I showed me and Stacy on Everett’s chromosomes.
It’s worth noting here that every segment is different. Triangulation on any individual segment should not be extrapolated to mean triangulation on every common segment, even between the same three people, is valid for all overlapping segments. Evaluate each overlap separately.
This fundamental change makes triangulation at 23andMe much more difficult for the genealogist. Fortunately, there is a work-around.
Please feel free to share this article with anyone who may have tested at 23andMe and is using their tools for genealogical purposes.
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