DNA Triangulation ? [closed]

Question

A grandchild, great grand & 2 2nd cousins 1x & 2x removed all match on Chromosome 14 from 73M to 89M on GEDmatch Matching Segment Matrix. Relationship finder for the 2 cousins goes back 3 generations to a common ancestor.  Does this constitute an Autosomal DNA triangulation?

Comments

Is the 2C1R and 2C2R parent/child to one another?  Also are the great grand child and grandchild parent/child?  If yes to these then no, this would not be triangulation.  The 3 (or more) legs of a triangulation group must meet at the couple you are attempting to triangulate to.  If one of the legs meets up with the other before, then those 2 legs become essentially one before continuing up to the ancestral couple you are seeking to triangulate on.

For example, I have my father, my kit, my grandmothers, a sibling to my grandmother, and we all have a segment shared with a 5th cousin.  I can't use myself, father, grandmother, sibling to my grandmother as separate legs because we meet each other way before we get up to the ancestral couple we are trying to triangulate with the 5th cousin on.

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Zack, yes the 2C1R & 2C2R are parent child. No the great grandchild is child of a 1st cousin of the Grandchild but the common ancestor between the later is earlier than the ancestor those two have with 2C1R.  Thanks for your help.

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I'm confused. I inferred from your question that Euphrasia Tuck is the common ancestor. You are the granddaughter and you have test results for a first cousin of yours and that cousin's son. If you have a good 1st-cousin match with your cousin, you don't need to even think about triangulation because you're confirmed.

So now I'm guessing that the common ancestors of interest are Euphrasia's parents (Edward and Fannie Sears). If you have good 2nd-cousin-level matches between yourself and a second cousin descended from one of Euphrasia's brothers (and similar good matches between your first cousin and that second cousin), then you can confirm your branch's and your second cousin's branch's connections to the great-grandparents.

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Do I  understand correctly, since two of Euphrasia’s granddaughters have tested and a great grandson, she can be confirmed by DNA?

 As for Euphrasia’s parents I will refer to your reply and work on them next.   Sorry for any confusion and thanks much for your help!

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One more detail that bears repeating: To confirm a grandparent based on DNA from grandchildren, the autosomal DNA match between first cousins needs to be in the predicted range for a first cousin match.

Answer 1

Hard to tell from the description you gave. It probably does constitute atDNA triangulation but I'd have to know more. One main question is: do you have paper documentation of the relationships?

Answer 2

Yes there is a paper trail.. yes blood relationship when running the Relationship Finder all back to the same common ancestor on Wikitree. Yes all four match each other on same chromosome ..  Do phased kits qualify for triangulation?

Comments

If the phased kits you refer to are Gedmatch "Lazarus" profiles or something similar (profiles created for a nontested person by assembling data for other people who tested), they cannot be used in triangulation.

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Thanks Ellen!  I did not know that...

Answer 3

FYI - Triangulation is not necessary for 3rd cousins or closer.