Interpreting triangulated chromosome matches

[Mart 'n' Al]

I have a half first cousin. We share a grandfather although our respective Fathers were born to different partners of the grandfather.

25 out of our top 30 matches triangulate with third people. 15 of those 25 triangulate on chromosome 12, between 8 and 24 cM.  What is the difference between those in the group of 15, and the other 10, who match us both, but NOT on chromosome 12?

Martin

[Craclyn]

The other 10 are shared matches who are not triangulating. They may be descended from the same set of ancestors or they may relate to you and your half first cousin through completely different lines.

[Mart 'n' Al]

Craclyn, I just want to clarify, in case it changes your reply, that the other ten do match me, and my cousin, and third people, but not on chromosome 12.  Does that mean the matches on chromosomes 11 and 16, (the next commonest matches) are different family branches to the group of 15, and to each other?

What about two of the 15 who match both me and my cousin, but on two separate chromosomes, Chr12 and another?

Martin

Martin

[Craclyn]

If you got segments from your common ancestors on chromosomes 12, 11 and 16, some of their other descendants may have got a mix of segments from them that only included one of those chromosomes. It does not necessarily imply a different branch, just that they did not get all of the same DNA as you did.