Have you heard the term “segment triangulation” associated with DNA and wondered what that meant? Perhaps you wondered if this could help you confirm an ancestor that you’ve researched? Which DNA testing and third-party companies offer this tool? In this article, I’ll define the term and show how the process can help you in your genealogy journey of discovering your genetic family tree.
Pedigree Triangulation
I previously wrote about pedigree triangulation and used the following visual from the ISOGG Wiki page to explain the concept. You and your DNA match both received DNA from your Most Common Recent Ancestor (MRCA). In pedigree triangulation, you compare your family trees to find the path back to the MRCA.
https://isogg.org/w/index.php?curid=4107
Segment Triangulation
Now let’s talk about segment triangulation. Although this also involves a triangle, in this case, we’re talking about three DNA matches. If two or more people match with a third person on the same segment of DNA AND they all match with each other on that segment of DNA then they each have likely inherited that shared segment of DNA from a common ancestor – if the connection is within a genealogical sound timeframe for DNA inheritance. The following image illustrates a triangulated match between my mother, Anna, and two DNA cousins who all share DNA on chromosome 7.
Segment triangulation is ideal, but not always possible. The amount of DNA you inherit from an ancestor decreases with each generation. Because the DNA randomly recombines with each generation, you will not inherit the same DNA segments from your grandmother as your first cousin. You’ll likely inherit some common segments, but not all.
When autosomal DNA began being used by genealogists, segment triangulation was the gold standard and no testing company had a tool. It required asking DNA matches to upload their raw DNA to GEDMatch for comparison and using spreadsheets to track the segment data. Two testing companies now offer a chromosome browser that shows triangulated segments, My Heritage and 23andMe. Additionally, DNA from all the testing companies can be uploaded to GEDMatch and the tools there used to find triangulated segments.
Nicole illustrated how to use chromosome browsers from each DNA test company in her article, “The Chromosome Browser: A Tool for Visualizing Segment Data.” She detailed segment triangulation on 23andMe, My Heritage, and GEDMatch. In this article, I’ll show how I discovered the triangulated segment illustrated above using the chromosome browser on MyHeritage.
Segment Triangulation on MyHeritage
When I viewed my mother’s list of DNA matches on MyHeritage, her top matches were me, my children, and a niece as expected. Her next closest match was her first cousin, Kathleen. Both women are now deceased but I know exactly how they are connected through their grandparents Charles Cannon Creer and Mary Margaret Peterson. MyHeritage provides several estimated relationships based on the 1,094 cM of shared DNA. With 34 shared segments, there is a good chance that my mother and Kathleen will have another DNA match who also shares one of those segments.
Shared match information for Kathleen, Anna’s 1st cousin
When I clicked on the purple “Review DNA Match” on Kathleen’s entry I was taken to a page that showed DNA matches between both Anna (on the left) and Kathleen (on the right). In the image below, notice how the shared match “W” could be a variety of relationships from the 1st to 2nd cousin range. At this point, I didn’t know who this cousin was, but MyHeritage had added an icon indicating a triangulated segment between Kathleen, “W” and Anna (highlighted by the red box).
W shares DNA with both Anna and Kathleen
Clicking on the icon indicating a triangulated segment, I was taken to the “Chromosome Browser – One-to-many” tool shown below. It highlighted a triangulated segment on chromosome 7. The segments that Anna and Kathleen share are in red and the segments that Anna and W share are in yellow. Clicking on the rectangle highlighting the triangulated segment, I saw that the shared segment size is 15.5 cM. Anna shares much more DNA with Kathleen than W as evidenced by the many red segments. If none of the segments had matched up, Anna wouldn’t have had any triangulated segments with Kathleen and W. This would not have precluded a genetic relationship; it just wouldn’t have been segment triangulation.
My Heritage, “Chromosome Browser – One-to-many,” database report, My Heritage (https://myheritage.com : accessed 8 August 2019), triangulated segment, Chromosome 7 Genomic position: 51077759 – 75614777, RSID: rs757323 – rs2302429, Segment size: 15.5 cM, Number of SNPs: 7,680.
How did I use this information in my genealogy? I noticed that Anna, Kathleen, and W were likely the same generation based on MyHeritage reporting their ages as “90s” and deduced they were probably 2nd cousins. I hypothesized that W is most likely a descendant of the ancestral couple a generation back, William Creer and Sarah Jane Miller who were Anna and Kathleen’s great grandparents.
The DNA match “W” appeared in a private tree managed by John Smith (privatized name) so I didn’t know his parents or his grandparents. I decided to do some investigating on the FamilySearch Family Tree for a possible match. William Creer and Sarah Jane Bradley had several children who lived to adulthood and also had large families. Any one of their grandsons could have been “W” and if he was still living he wouldn’t appear on the family tree. I needed more clues to discover the identity of “W.”
Fortunately, MyHeritage allows you to click on any DNA match and see how they are connected to your shared matches. When I explored the shared matches for W I found “Phebe Smith” listed toward the top. She was a 3rd – 5th cousin to my mother but was W’s daughter! She had an unusual first name and it appeared her husband John Smith managed W’s kit. A Google search found her mother’s obituary and gave me the name of W. Based on the various clues of age, name, location, and predicted relationships I placed W in the family as a likely 2nd cousin to my mother and to Kathleen. Now I can continue to research the family and discover W’s line to William Creer and Sarah Jane Bradley.
Hypothesized placement of W and his daughter Phebe in the family tree.
To check my hypothesis, I can contact the administrator for the account of William Creer on MyHeritage and verify the tree, but this triangulated match is strong evidence of my mother’s relationship to her great grandparents. The triangulated segment that she, Kathleen, and W share on chromosome 7 almost certainly came from either William Creer or Sarah Jane Bradley.
The screenshot below illustrates my mother’s tree to William Creer and Sarah Jane Miller and it’s nice to know that DNA evidence confirms this relationship.
If you’re new to working with your DNA results, I recommend that you try segment triangulation with an easy project such as confirming a set of great grandparents as I did in this example. You’ll be more familiar with the names and will probably recognize some of your close DNA cousin matches. Experiment with the segment triangulation tools on My Heritage, 23andMe, and GEDMatch. As you get more comfortable with the concept and tools, you can use segment triangulation to prove additional ancestors in your family tree.
Best of luck in all your genealogical endeavors!
Other articles in the Research Like a Pro with DNA series:
Step 1 Take a DNA Test: Which DNA Test Should I Take? and DNA-Recommended Testing Strategy
Step 2 Assess: Understanding and Using Your DNA Results – 4 Simple Steps
Step 3 Organize: Seeing the Big Picture: 3 Ways to Chart Your DNA Matches
Step 4 Research Objective: What Do You Want to Know? 3 Steps to Focus Your DNA Research
Step 5 Analyze your Sources: DNA Sources, Information, and Evidence: Sorting it All Out
Step 6 Locality Research: Where in the World Has My DNA Traveled? DNA and Locality Research
Step 7 Research Planning: Genealogy Research Planning with DNA
Methodology and Tools to use as you plan your research:
– Charts for Understanding DNA Inheritance
– Clustering or Creating Genetic Networks
– Pedigree Triangulation
– Chromosome Browsers
– Segment Triangulation – You Are Here
– Chromosome Mapping
– DNA Gedcom
Step 8 Source Citations: DNA Source Citations
Step 9 Research Logs: DNA Research Logs: how to keep Track of Genetic Genealogy Searches
Step 10 Report Writing: DNA Research Reports – the Ultimate Finish
Step 11 What’s Next? Continue Your Research & Writing, Productivity, and Education
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