Should I test my patrilineal 3rd cousin ?

[Lklundin]

I have managed to get in contact with several 3rd cousins (actually 3rd cousins of my father, so I am their 3C1R).

I have offered them all a Family Finder test to support the claim of the traditional genealogy (and so far all have been FF-matches with my father in the expected cM range).

Now, one of those 3rd cousins and my father are related via their patrilineal GGFF.

I was the first in my family to take a FTDNA test, so I took the Y-DNA-67 (+FF+FMS) test. I have not bothered to get a Y-DNA test for my father as well, because I have many other testing candidates, I have no close Y-DNA matches - and perhaps one day there will be an affordable full Y-DNA test.

Combined with the traditional genealogy I consider the FF-match between my father and his patrilineal 3rd cousin sufficient to not doubt their relationship, so I don't want get this cousin a Y-DNA test just to test the relationship.

But if I did get this 3rd cousin a Y-DNA-67 test, then I believe we are distantly enough related that we may have a genetic distance of 1 or even more (as opposed to just being identical).

What could I learn from getting a Y-DNA test from my fathers patrilineal 3rd cousin?

Thanks,
-Lars.

[prairielad]

In my personal opinion it could be beneficial to test another known line's ydna of the same surname.

This will rule out any recent mutations in lines since common ancestor.

YDNA timeframe is based on the average mutation rate of markers, it is possible that one line can have a higher then average rate which will place possible common ancestor further back in time according to the Genetic Distance Timeframe.

If you have no close matches this could be the case

My line for example has had this happen. My father and his 1st cousin tested to the 67 level and the results give them a GD of 4. Common ancestor was their Grandfather.

According to results it shows that my line has had 2 markers mutate (1 being a possible 2 Step mutation),
Another marker(CDY) also has a mutation which is a 50/50 chance of being either line according to surnames groups results for this marker.
It also shows that our lines share a common mutation on a 4th marker which can be dated to happen in their Grandfather(1850) or earlier which seperates or lines from all other surname matches.

At the 67 level my fathers kit has GD's of 4 to 7 with matches while his cousins kit is has GD's of only 1 to 4.

[Lklundin]

it is possible that one line can have a higher then average rate

Many thanks for giving me this insight.

-Lars.