Can y-DNA be used to establish paternity between siblings several generations back?

[drewsg]

Lets say I have a doubt about whether my great-grandfather had the same father as his brothers. If I were to find male descendants of his brother to get y-DNA tested, would it tell me whether or not they had the same father?

[mabrams]

It sounds like you would like to test a potential 3rd cousin with a common great great gf. A YDNA test would likely be a very tight match. 37/37 is possible. Or 110 or 111 out of 111.

In general, a YDNA test can "rule out" but only be plausible on the "ruling in" side. That does not apply as much on 3rd cousins.

You should be aware that even a 37/37 only indicates that you and your potential third share a Y ancestor. It does not explicitly confirm that your great grandfathers were brothers. I have gotten 111/111 with a 4th cousin.

You can also reinforce Y matching with autosomal testing, since 3rd cousins normally (over 90%) match.

The other approach to Y testing is SNP testing, like a BigY700 or a SNP Pack or as part of 23andMe. This is probably not necessary for third cousins, although if you both get the super common R-M269, you might want to refine that. You could also test for SNPs, if the Y37 is surprisingly weak, like 33 or 34 out of 37.

[drewsg]

It sounds like you would like to test a potential 3rd cousin with a common great great gf. A YDNA test would likely be a very tight match. 37/37 is possible. Or 110 or 111 out of 111.

In general, a YDNA test can "rule out" but only be plausible on the "ruling in" side. That does not apply as much on 3rd cousins.

You should be aware that even a 37/37 only indicates that you and your potential third share a Y ancestor. It does not explicitly confirm that your great grandfathers were brothers. I have gotten 111/111 with a 4th cousin.

You can also reinforce Y matching with autosomal testing, since 3rd cousins normally (over 90%) match.

The other approach to Y testing is SNP testing, like a BigY700 or a SNP Pack or as part of 23andMe. This is probably not necessary for third cousins, although if you both get the super common R-M269, you might want to refine that. You could also test for SNPs, if the Y37 is surprisingly weak, like 33 or 34 out of 37.

Thank you for your response!

I have a 1C2R on 23andMe. He would be the son of my great-grandfather's youngest brother but his haplogroup shows up as L-48. Mine shows as R-S764 on 23andMe, but my y-111 says R-M269. That's what initially piqued my interest in addition to my great-grandfather not having any father listed on his birth certificate and my matches to his siblings' descendants being relatively weak.

I'll have to do more digging to fully understand y-DNA testing.

[Stevo]

Thank you for your response!

I have a 1C2R on 23andMe. He would be the son of my great-grandfather's youngest brother but his haplogroup shows up as L-48. Mine shows as R-S764 on 23andMe, but my y-111 says R-M269. That's what initially piqued my interest in addition to my great-grandfather not having any father listed on his birth certificate and my matches to his siblings' descendants being relatively weak.

I'll have to do more digging to fully understand y-DNA testing.

If that's right, that he is R1b-L48, and you are R1b-S764, then you do not share a Y-DNA ancestor in common, not for the last several thousand years, anyway, and certainly not someone as recent as your second great grandfather.

If you look at the R1b-L51 descendant tree graphic below, you will see that the last Y-DNA ancestor you shared in common with your alleged 1C2R was Mr. L151, and he was born about 5,000 years ago. Your R1b-S764 haplogroup descends from R1b-P312, while R1b-L48 descends from R1b-U106.

Your most recent common ancestor probably rode with Yamnaya, or at least Corded Ware.

R1b-L51 Descendant Tree.jpg

[mabrams]

Regarding your different haplogroups, which came from the two types of Y tests.

Haplogroups are based upon Y-SNP tests.
A Y111 is a Y-STR test. FTDNA will make a very basic haplogroup prediction, such as R-M269, but will not attempt an adv prediction.

23andMe does test a sampling of key SNPs, which is how you got L48 and RS764. These are not compatible as Stevo's chart shows, although they are both descendants of R-M269.

It's a little confusing since you have results from two different men from two different types of Y tests from two different companies.

FTDNA does sell adv SNP testing in several ways, primarily as the BigY.

[Stevo]

The SNP S764 is downstream of the SNP L1335. Well before anyone knew about L1335, John McEwan identified a 37-marker STR haplotype cluster he named STR47 - aka "The Scots Modal Haplotype", so named because it is common among men of Scots descent. Here it is, in FTDNA order:

R1bSTR47 13 24 14 10 11 14 12 12 12 13 13 30 18 9 10 11 11 25 15 19 30 15 15 17 17 11 12 19 24 16 15 18 17 37 38 12 12

When the SNP L21 was rediscovered, in 2008, as I recall, guys who belonged to the Scots Modal cluster found that they were L21+. Subsequently, when L1335 was discovered downstream of L21, the possessors of the Scots Modal tested L1335+. I believe that trend continued when L1065 was found downstream of L1335 (and S764 is also downstream of L1065).

I was around back when all that was going on, but I don't recall all the details and all the refinements. The point I'm getting at is that S764, I believe, is very frequent among Scots.

[Stevo]

Hey, drewsg! Where'd you go?