DNA Segment Triangulation

By Kitty Cooper

blog. kittycooper. com

What is a DNA segment?

Ancestry DNA can be uploaded to any or all of these sites to see segment matches in a chromosome browser:

  • GEDmatch.com
  • MyHeritage.com
  • FamilyTreeDNA.com $

5 cousins compared, but do they match each other

ISOGG wiki entry for Triangulation


  • When three people all match each other at the same autosomal DNA location we call it Triangulation.
  • From ISOGG: "If you have at least three people with a common ancestor matching on the same segment then you can infer that the segment came from that ancestor. "
  • Inversely, if three people all match each other on the same good sized segment then you can infer they have a common ancestor.(larger than 7cM but 11cM or bigger is preferred)
Use https://dnapainter.com/tools/sharedcmv4 to calculate the likely relationships





















KRISTINE v my cousins

Kristine compared to Mike and John on chromosome 11


Chr 11

Kristine compared to John, George and Henry

John versus 2nd cousins
George (PG) and Henry

Chr 14


Kristine compared to Mike and Katy

Mike versus Katy

Chr 16

More recently I found a grand daughter of Charley and got her, MM, to test too








The total number of cMs seemed low until I realized that she was from a different wife of Charley so a HALF 1C2R

Only one of the five segments MM shares with Kristine is in the same location as the other cousins, the one on chr 11, does it triangulate?

Kristine compared to Mike and John on chromosome 11

John vs Mike

Chr 11

WOLD homestead 2015 in Vestfold, Norway


Make a Master Spreadsheet of your segment matches

Template available in my downloads area http://blog.kittycooper.com/?ddownload=2556

GenomeMate is another way to organize this data as is DNApainter.com

Every company but ancestry will give you the segment information in this format or similar - you can cut and paste into your spreadsheet

Add the columns you need, Match name, GEDmatch number,MRCA ...

My fourth grandparents lived on VE farm in Etne , Hordaland and I have a triangulation group for the cousins descended from them

I told Shelley she triangulated into that group very small so probably too far back to find. She replied my great grandmother was Anna VE ... so I found that we are 5th cousins once removed

Decided to investigating LuAnn, a new match with a surname of interest, Brekke 

LuAnn matches dad and my brother but not me or either 2nd cousin

Another way to triangulate is to use other known relatives. Sometimes my brother and I got opposite side segments from Dad

These are my dad's matches: Everyone marked M for maternal matches my brother Shipley, but the P for paternal matches me

Comparing LuAnn to the matches on each side of her in the spreadsheet she matches just Lester

Since LuAnn matches Ship and Lester she must be maternal and since my brother matches Katy here, she is related on the WOLD line


(Chromosomes without matches removed)

Gunnar versus my brother

Top matches Dad has in common with Gunnar

Gunnar versus Kitty, no match on 2, match on 20

Dad's Matrix Matches

How to get a Chromosome Browser Results (CBR) file from Family Tree DNA for the DMT tool

DMT output as a CSV

DMT output as a CSV

Automated Triangulation Tool at GEDmatch.com

GEDmatch triangulation sorted by chromosome location

Gedmatch Triangulation for Dad sorted by Match Name

Cousin Katy

Gedmatch Triangulation for Dad cut and pasted to a spreadsheet then sorted by chromosome and start

When you look at your shared matches at MyHeritage, this icon to the right of the match tells you there is at least one segment that triangulates
The icon
When you click on that triangulation icon you get a page like this where the matching segments are shown with the triangulating ones outlined


DNA Triangulation -2018 fall

By Kitty Cooper

DNA Triangulation -2018 fall

How to use triangulation to confirm DNA relatives

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