Wednesday, March 31, 2021

Gina's Journey - Part 5: Using Triangulation

DNA Triangulation
Let’s backup a bit here and explain the process of Triangulation. The short explanation for triangulation is comparing the results of three DNA matches who are not closely related to find a shared segment on the same chromosome with the length of 7 centimorgans or greater. A length of less than 7 cMs might be a false match and therefore should be discounted.

An overlapping match on the same segment with greater than 7 centimorgans indicates all three DNA cousins share a common ancestor. The best way to view this three-way comparison is by using a chromosome browser (available through 23andMe, MyHeritage and GEDmatch). If the matches you are using for triangulation as well as your own results have attached, well-researched family trees, you can compare the three trees and hopefully find the most recent common ancestor (MRCA) shared between the three DNA cousins.

If you are utilizing the tools at DNA Painter for analysis, “paint” this specific chromosome segment onto your DNA map and assign it to the MRCA shared by you and your two matches.

Let’s simplify this in terms relating to Gina – by finding a shared, overlapping piece of DNA between myself, Gina and another cousin, I had found an ancestor who could be Gina’s birth father’s 2nd great-grandmother! This was still a wide span of four generations, but I was inching closer!

Glancing once again at my chromosome browser displaying shared centimorgans for two DNA cousins in a colorful spread of purple and orange bars, it was apparent I had more in common with both Gina and Debra than just that one great-grandparent! But our section of shared cMs on chromosome 20, although small, was confirmation that I was on the right track!

DNA Triangulation


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