My first DNA triangulation

Question

I think I've just identified my first triangulation, but I want to ask here if I'm doing it right.

The three parties are Garrigues-341 (my paternal uncle), Pendley-170, and Roland-729.

I've already determined that Garrigues-341 and Pendley-170 are 2nd cousins once removed. Gedmatch MRCA was 3.2 and 181.1 CMs in 8 segments.

Roland-729 is Garrigues-341's 6th cousin and Pendley-170's 5th cousin once removed. MRCAs are 4.8 in both cases. with 18.1 cM and 18.4 cM respectively. These are mostly the same DNA. Does that matter?

Answer 1

"Mostly the same DNA" isn't sufficient. Is there are least one segment greater than 7 cM that all three of them share with one another? That's what is required for triangulation. The GEDmatch IDs for by Garrigues-341 and Pendley-170 are displayed on your profile, but the privacy level for Roland-729 is 'private' so her GEDmatch ID isn't visible, so I can't check for you to see if there is at least one shared segment for all three.

Comments

Roland-729 is A817602.

I think I'm good, but since it's my first triangulation, I just want to be certain.

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Which chromosome and segment do all three share and how long is the common segment in cM?

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Chris, On GEDmatch if you run the 3D chromosome browser (under 'analyze your data') with the three GEDmatch IDs, and look at the very last section at the bottom of the page, 'segment details', you can see that all three share a 10.9 cM segment. It's on chr 17 from 3,420,695 - 7,848,110. If you run the 'relationship finder' for each to one another you can figure out which relationships can be marked 'confirmed with DNA'. Be sure to put a statement on the page of each child whose parent you give the relationship status 'confirmed with DNA'. Here's the page that gives you an example of how to write the statement: https://www.wikitree.com/wiki/Help:DNA_Confirmation#Autosomal_Triangulation  If it's okay with the test takers, I recommend that you change their privacy levels from 'private' to 'private with public biography and family tree' so that everyone can see how they're all related. Let me know if I can help.

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Chromosome 17 from 3420695 to 9904694, 18.1 cM

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Thanks, Kay!

I'd started writing my previous comment before going to lunch and hadn't seen yours.  Sounds like I did it right.  I'll work on getting it properly documented in wikitree now.

This is great.  Now I want to find another one!

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Interestingly it looks like if I'd used my kit (A034934) instead of my uncle's the section of DNA is longer. 

3651232

10060647

18.3

I used his because I assumed since he was a generation closer he'd have a better match.

Ether way, it's good enough to triangulate and I'm happy.  Thanks again.

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You're correct, that generally the person a generation closer will share more DNA. But if your father inherited a larger segment of Chr 17 than his brother, and passed it on to you, then that would make sense that you have a larger segment than your uncle does.

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But the triangulation is the longest segment shared by all three, so it doesn't make sense to say one is shorter than another, all three should be the exact same length, so probably the shorter of the 2 you listed.

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One more question. How long does the segment need to be to be considered a match?

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According to this page, 7 cM for a triangulated match.