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Might you share a Powys Y-DNA?

11th Nov 2022

Two Powys descendants of a man who was born in 1649 have been found to have identical Y-DNA. Y-DNA is a sex chromosome and is only carried by males. Y-DNA does not combine with any other DNA and is the male sex chromosome. The female sex chromosome is X and behaves slightly differently. Anyhow this feature of a Y chromosome enables us to say that the Y gene will not be changed from father to son.

But us humans are a bit contrary. We, a few of us, engage in NPE, non-paternal-events, where the mother consorts with someone who is not her apparent partner. Yes, any male child inherits his father's Y-DNA, but it may not be the father that he may have been brought up to believe to be such.

I have seen it written that 10% of male births are from NPEs. If true, then a mere 90% of sons at each generation will inherit their apparent father's Y-DNA. After two generations this is 81%, and so on.

The above two Powyses have the same Y-DNA. So none of the mothers in the seventeen generations that separate them did any NPE. Remarkably, they 100% have the same Y-DNA and we can therefore say that this must have been the Y-DNA that the ancestor born in 1649 carried and acquired at his conception around 1648. See the accompanying tree.

The elder descendant is 8 marriages from Sir Thomas, and therefore has a 43% chance of breeding with Y-DNA unchanged. The younger descendant is 9 marriages from Sir Thomas and has a 38% chance of breeding unchanged. The combined chance of both of them having identical Y-DNA is 17%.

With such a low chance, you can see why I think it quite remarkable that we do have a DNA identity between us. It is probably to do with the social climate in the intervening generations; might chastity belts have been employed?

Or, of course it might be that this is not quite so unusual and the 10% of NPE events does not apply.

Anyhow it is a good reason to suggest that some others might join in to see if they carry the same Y-DNA. The obvious candidates are other male-line descendants of Sir Thomas. The more that do such a test the better view we will have of what percentage of apparent male lines have a NPE in them.

There are more obvious candidates. As Sir Thomas carried this Y-DNA, his brothers and the brothers of his father and of the male line ancestors of his father should all have carried it. This last investigation does not need genealogical research. If you think there is a chance you carry this Y-DNA, then a test will decide it absolutely regardless of the apparent or lack of any documentation. If you have this DNA then you share ancestors with Sir Thomas Powys, full stop, incontrovertibly, God's own truth.

The Y-DNA concerned has the name of R-FT287223. The only firm offering Y-DNA tests that I know of is FamilyTreeDNA.com

You can contact me at tim@powys.org

Tim Powys-Lybbe
8th November 2022

Family tree appended.

A couple of links that can also be found on the free links page.

Know your DNA    DNA Testing Guide


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