Quote Originally Posted by O'Callaghan View Post
This is similar to my situation. I have two uncles (my mum's brothers) who are the last male O'Callaghans of the name in our family. One never married, and the other married someone who already had a daughter and didn't want more children. They are both well into their eighties, so there's no likelihood that either of them will have a genetic son now.

I would love to know what a DNA test on either one of them would show, but I am hesitant to ask them to get tested. I doubt if they would immediately realise that it would only take a scraping from under the tongue (or so I've heard). OTOH, if it is left too long, then eventually it will be too late, for the saddest of reasons. I think I ought to speak to my mum about this. She is the family genealogist anyway, so she would be interested in the results I'm sure.

The burning question that it ought to answer is whether we are all descendants of Ceallachan of Cashel, King of Munster, d.953, or simply, as we already know, descended from a long line of Irish sailors. Whether a Y DNA test could even answer that I'm not sure, but the only way to really find out is to test one of my uncles.
Theis no scientific way to prove it, even if you have yDNA profile on Ceallachan of Cashel or one of his direct patrilineal verified relatives, your paper trail is far more likely to yield results. YDNA on your uncles would be helpful for you to trace that particular lineage and see if it matches up with those of other callahans, particulalry in sizable numbers in the local where that ancestor hailed from. If one of them could prove descendency then you might be in luck, but still all you have proved is that you and the other person with the matching profile have at least one common ancestor, not necessarily that it actually is Ceallachan. It could be anyone who he shared a common male ancestry with, potentially generations above even Ceallachan---his father, uncle, nephews, grandfather, great grandfather, their other siblings or uncles or nephews, etc... All yDNA profiling proves is common ancestry on the male lineage side of SOME SORT, not any specific sort.