Recently, I published the article, Hitting a Genealogy Home Run Using Your Double-Sided Two-Faced Chromosomes While Avoiding Imposters. The “Home Run” article explains why you want to use a chromosome browser, what you’re seeing and what it means to you.
This article, and the rest in the “Triangulation in Action” series introduces triangulation at FamilyTreeDNA, MyHeritage, 23andMe, GedMatch and DNAPainter, explaining how to use triangulation to confirm descent from a common ancestor. You may want to read the introductory article first.
This first section, “What is Triangulation” is a generic tutorial. If you don’t need the tutorial, skip to the “Triangulation at MyHeritage” section.
What is Triangulation?
Think of triangulation as a three-legged stool – a triangle. Triangulation requires three things:
- At least three (not closely related) people must match
- On the same reasonably sized segment of DNA and
- Descend from a common ancestor
Triangulation is the foundation of confirming descent from a common ancestor, and thereby assigning a specific segment to that ancestor. Without triangulation, you might just have a match to someone else by chance. You can confirm mathematical triangulation, numbers 1 and 2, above, without knowing the identity of the common ancestor.
Reasonably sized segments are generally considered to be 7cM or above on chromosomes 1-22 and 15cM or above for the X chromosome.
Triangulation means that all three, or more, people much match on a common segment. However, what you’re likely to see is that some people don’t match on the entire segment, meaning more or less than others as demonstrated in the following examples.
You can see that I match 5 different cousins who I know descend from my father’s side on chromosome 15 above. “I” am the grey background against which everyone else is being compared.
I triangulate with these matches in different ways, forming multiple triangulation groups that I’ve discussed individually, below.
Triangulation Group 1
Group 1 – On the left group of matches, above, I triangulate with the blue, red and orange person on the amount of DNA that is common between all of them, shown in the black box. This is triangulation group 1.
Triangulation Group 2
Group 2 – However, if you look just at the blue and orange triangulated matches bracketed in green, I triangulate on slightly more. This group excludes the red person because their beginning point is not the same, or even close. This is triangulation group 2.
Triangulation Group 3 and 4
Group 3 – In the right group of matches, there are two large triangulation groups. Triangulation group 3 includes the common portions of blue, red, teal and orange matches.
Group 4 – Triangulation group 4 is the skinny group at right and includes the common portion of the blue, teal and dark blue matches.
Triangulation Groups 5 and 6
Group 5 – There are also two more triangulation groups. The larger green bracketed group includes only the blue and teal people because their end locations are to the right of the end locations of the red and orange matches. This is triangulation group 5.
Group 6 – The smaller green bracketed group includes only the blue and teal person because their start locations are before the dark blue person. This is triangulation group 6.
There’s actually one more triangulation group. Can you see it?
Triangulation Group 7
Group 7 – The tan group includes the red, teal and orange matches but only the areas where they all overlap. This excludes the top blue match because their start location is different. Triangulation group 7 only extends to the end of the red and orange matches, because those are the same locations, while the teal match extends further to the right. That extension is excluded, of course.
Matches with only slight start and end differences are probably descended from the same ancestor, but we can’t say that for sure (at this point) so we only include actual mathematically matching segments in a triangulation group.
You can see that triangulation groups often overlap because group members share more or less DNA with each other. Normally we don’t bother to number the groups – we just look at the alignment. I numbered them for illustration purposes.
Shared or In-Common-With Matching
Triangulation is not the same thing as a 3-way shared “in-common-with” match. You may share DNA with those two people, but on entirely different segments from entirely different ancestors. If those other two people match each other, it can be on a segment where you don’t match either of them, and thanks to an ancestor that they share who isn’t in your line at all. Shared matches are a great hint, especially in addition to other information, but shared matches don’t necessarily mean triangulation although it’s a great place to start looking.
I have shared matches where I match one person on my maternal side, one on my paternal side, and they match each other through a completely different ancestor on an entirely different segment. However, we don’t triangulate because we don’t all match each other on the SAME segment of DNA. Yes, it can be confusing.
Just remember, each of your segments, and matches, has its own individual history.
Imputation Can Affect Matching
Over the years the chips on which our DNA is processed at the vendors have changed. Each new generation of chips tests a different number of markers, and sometimes different markers – with the overlaps between the entire suite of chips being less than optimal.
I can verify that most vendors use imputation to level the playing field, and even though two vendors have never verified that fact, I’m relatively certain that they all do. That’s the only way they could match to their own prior “only somewhat compatible” chip versions.
The net-net of this is that you may see some differences in matching segments at different vendors, even when you’re comparing the same people. Imputation generally “fills in the blanks,” but doesn’t create large swatches of non-existent DNA. I wrote about the concept of imputation here.
What I’d like for you to take away from this discussion is to be focused on the big picture – if and how people triangulate which is the function important to genealogy. Not if the start and end segments are exactly the same.
Each of the major vendors, except Ancestry who does not have a chromosome browser, offers some type of triangulation solution, so let’s look at what each vendor offers. If your Ancestry matches have uploaded to GedMatch, Family Tree DNA or MyHeritage, you can triangulate with them there. Otherwise, you can’t triangulate Ancestry results, so encourage your Ancestry matches to transfer.
Let’s start by looking at triangulation at MyHeritage.
Triangulation at MyHeritage
MyHeritage offers triangulation integrated into their chromosome browser.
At MyHeritage, select DNA Matches from the DNA dropdown menu, then click on the purple “Review DNA Match” of the person you want to compare. We re looking at my cousin, Cheryl F.
When reviewing my DNA match with Cheryl, I can see the list of people that Cheryl and I both match, including my mother, first on the list. In addition to my mother’s relationship to me, I can also see an estimate of how closely my mother matches the other person – in this case, Cheryl. Cheryl is my mother’s first cousin (1C) and my first cousin, once removed (1C1R.)
For triangulation, the important image is the little purple icon at right, above.
Clicking on the purple triangulation icon shows the segments where Cheryl, my mother and I all three match and triangulate.
Finding my mother among Cheryl’s close matches tells me immediately which parent I share with Cheryl.
The areas on the chromosome browser below in the rounded squares are triangulated, meaning that I match Cheryl and the other person (who just happens to be my mother) on that same segment.
Showing triangulation with Cheryl and my mother provides a great example, because of course I triangulate with Cheryl and my mother on every segment where I match Cheryl – because I inherited all of those segments through my mother.
However, as far as triangulation goes, the fact that two of those people are closely related, me and my mother, makes it the same as only two people matching – Mom and Cheryl. Still, since Mom and Cheryl are first cousins, that match confirms my great-grandparents.
Cheryl carries pieces of my great-grandparent’s DNA that my mother doesn’t though, so matches in common with Cheryl may prove very genealogically useful.
At the top right of this chromosome browser page, I can “add or remove DNA matches” from my match list. I can look through my match list to find another close relative to see if they triangulate or I can download my match list to see who else matches me on that same segment. Instructions for the file download are at the end of this section.
Same Segment Matches
To illustrate that people will match you on the same segment, but don’t match each other because they descend from different sides of your family, I’ll add some cousins from my father’s side of the family.
I’m going to select cousins Charlene and David, and remove my mother.
Below, we show chromosome 3 again, but the triangulation bracket is gone. This tells us that this segment does NOT triangulate between me and ALL three people.
Please note that I may triangulate with some of the people. The absence of the bracket only means that I don’t triangulate with ALL of them.
I already know that while I match Cheryl, Charlene and David on this segment, only David and Charlene match each other because they are both from my father’s side, and Cheryl doesn’t match either of them because she is on my mother’s side.
To prove this, and to determine triangulation groups, I can compare the people two by two and continue adding people to see if they continue to triangulate.
Below, I’ve removed Cheryl, and I triangulate on chromosome 3 with both Charlene and David. The triangulation bracket appears.
Therefore, I know that Charlene and David descend through one of my parents, and Cheryl through the other – even if I didn’t know anything else at this point.
To reiterate, triangulation at MyHeritage means triangulation with everyone showing at the same time on the chromosome browser.
Other Resources to Identify Common Ancestors
For additional information, I can check the match information with each person to see if our trees, surnames or locations intersect.
SmartMatches and Theories of Family Relativity each provide clues and help to explain why we might triangulate.
SmartMatches tell you that you and another person share an ancestor in your and their tree, BUT, that common person may not be a direct ancestor of one or both of you. You also may or may not be DNA matches, and if so, your DNA match may or may not be through that ancestor.
Theories of Family Relativity (TOFR,) on the other hand, tell you that not only do you have a DNA match with this person, but that you have a common ancestor, and who that ancestor is. Sometimes the connection is made for you, even if one or both of you don’t show that ancestor in your tree simply because you have not extended your tree back far enough in time.
I wrote about how to use Theories of Family Relativity here.
You can request to download your matches list and also your shared DNA segments at MyHeritage by clicking on the three dots to the right at the top of your match list, then click on the option you wish. The resulting files will be e-mailed to you a few minutes later. If they don’t arrive, be sure to check your spam filter.
Downloading your match list and/or shared DNA segments is NOT the same thing as downloading your raw data file to upload elsewhere. You’ll find those instructions in the Transfer section later in this article.
What About You?
Do you have a tree at MyHeritage?
If not, click on Family Tree to create or upload one including not only direct line ancestors, but their children and grandchildren which facilitates and encourages the formation of Theories of Family Relativity.
Connecting Your DNA to Your Tree
Assigning your kit and those of family members to the proper profile card in your tree is very important, especially for the formation of Theories of Family Relativity
If a DNA kit is not associated with an individual that is connected to ancestors, this reduces the probability that MyHeritage will be able to find a theory.
For example, if I took a DNA test but only have myself in the tree, not connected to my father and mother, but my father appears in another user’s tree (and there are more ancestors in that tree) MyHeritage won’t be able to find the information to generate a theory.
If I add my father, then the system has a common ancestor to work with.
When the TOFR algorithm runs, it’s trying to find any possible route to connect the two individuals (you and your DNA Match). If you are associated with individuals in multiple sites or trees, MyHeritage will try all of them and generate multiple paths for you to evaluate.
Have you assigned the kits of family members you manage to the proper place in your tree?
You can do this easily under the Manage DNA Kits option, under the DNA tab. Click on the three little dots to the right of the kit.
Then click assign the kit.
You’ll be prompted
If you start typing, you’ll be prompted with the names of people in your tree.
Other Resources to Identify Common Ancestors
MyHeritage includes other tools to help you identify common ancestors as well, including:
- SmartMatches where MyHeritage matches individuals in trees
- AutoClusters showing groups of people that match you and each other
- Shared Matches indicating common DNA matches between you and another DNA match
- Shared Ancestral Surnames show common surnames, even if a common ancestor does not show in a tree
- Shared Ancestral Places indicating common locations in trees
- Shared Ethnicities comparing ethnicity between matches, a feature typically only beneficial if looking for a minority (to you) ancestry match
- Genealogical Records including matches from other databases such as Geni.com and FamilySearch
The article, Are You DNA Testing the Right People? explains how to determine who to test. Make sure you aren’t missing anyone that you need.
Here’s how to transfer:
- Ancestry Step by Step Guide: How to Upload-Download DNA Files
- 23andMe Step by Step Guide: How to Upload-Download DNA Files
- MyHeritage Step by Step Guide: How to Upload-Download DNA Files
- Family Tree DNA Step by Step Guide: How to Upload-Download DNA Files
Most of all – have fun!
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Thank you so much.
DNA Purchases and Free Transfers
- MyHeritage DNA only
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- MyHeritage FREE DNA file upload
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