Genetic distance of one at 67 markers, what next?

[k.o.gran]

Hi all,

I'm seeking some advice on what to do next based on current results. I started with DNA testing to try to find out who my great great grandfather was. All I had to go by was his name in the Norwegian church records from my great grandfather's birth, and the family rumor that he was Scottish. In the beginning, I didn't get any useful results other than a lot of Scottish Family Finder results that indicated the rumor was true. However, one of my matches was kind enough to help me with the research in Scotland, and she found a plausible candidate (let's call him "PL"). Through a lot of research I was able to prove that "PL" sailed the coast of Norway nine months prior to my great grandfather being born. "PL" was born in Dundee in 1838. I focused on finding living relatives of "PL" for a Y-DNA test, but no such luck yet.

Then I got a match at a GD of 2 at 67 markers (let's call this match JD). She could trace her paternal line to a man born in 1871 just outside Dundee to an unnamed father and was looking for the same thing as me. I had my second cousin tested and he is GD1 with me and GD1 with "JD".

These are the markers we mismatch on:

    - DYS456 - DYS534
Me  -   17   -    15
2nd -   18   -    15
JD  -   18   -    16

2nd is my second cousin. All other 65 markers are equal.

Could "PL" or one of his brother's be "JD's" ancestor (the unnamed father)? Would the Family Finder give us any info here? If "PL" is the unnamed father, my father and "JD" would be "half second cousins" and "full" third cousins. If it's one of "PL's" brothers, they will be "only" third cousins. Will Family Finder be able to differentiate? The reason I use my father as an example here is because he has done the Family Finder test already. JD has only tested Y-DNA.

All advices are very welcome and thank you to all who found the time to read all this.

-Kai

[thetick]

I doubt FF would be able to guarantee to tell you the difference between "half second cousins" and "full" third cousins. You may get a more likely answer , but it would not be definitive. IF you can test the 1/2 of family you suspect that is unique with the 2nd half cousin then you could get a definite yes or another not completely sure.

[k.o.gran]

IF you can test the 1/2 of family you suspect that is unique with the 2nd half cousin then you could get a definite yes or another not completely sure.

Hi thetick,

I'm not sure I understand what you mean here. The reason I end up with "half" second cousins is because the persons in question would have the same great grandfather, but not the same great grandmother.

Another part of the question is if it's reasonable at all to suspect the connection is that close. In other words, is it likely that DYS534 would mutate in three to four generations.

Thanks,
Kai

[thetick]

There have been parent sons documented with two and even three markers different, but obviously this is not common, but possible.

[mkdexter]

Family Finder would not tell you the difference between half second cousins and full third cousins. To the test they are about the same thing with the second cousins only slightly being higher (like 150cM vs. 80cM) in shared cM but not enough to distinguish the difference with accuracy. Recombination could very easily cut your 150cM of half second cousins down to 70cM which would be a 3rd cousin and you would never know it.

Try to find a living relative of PL if you can and start with the Y DNA test.

Matt.

[k.o.gran]

Thank you Matt and thetick.

Try to find a living relative of PL if you can and start with the Y DNA test.

Easier said than done, but I'm trying.

-Kai