My links to Clan Callaghan are through my mother, so to verify this through DNA we would have to check one of a couple of elderly uncles, while they are still with us. OTOH, there's really no point in bothering them, as she has already traced the genealogy to the 'correct' county (Cork) in Ireland where the clan lands were located, and no reason to think we are in any line leading of succession to the chief. IOW, there's no need to prove that I'm a member of that clan, because I already know I am.

There again, so little is known of my father's family, beyond their immediate origins in London and nearby, that it might prove interesting to test my own yDNA and see what comes up. My mother has been known to joke that my father looks Jewish, and his counter is that he may be of Roman descent, which is not entirely fanciful, as it was the Romans who founded London, ever so long ago. Fortunately, I seem to have inherited her nose rather than his, no offence intended to anyone. I have a common enough English surname, but one that also has Spanish and Italian variants. Of course, in general the English did not have surnames until centuries after the Romans left, even though Romans and Romanised Britons did have surnames. Or maybe my mum is right on where that branch of the family originated. Unknown Jewish origins might be possible to isolate more or less in DNA, Roman origins not so much, or perhaps might not be distinguishable from the former or from, say, more recent Italian descent, but who knows where it might lead. I'm getting ahead of myself with no real data, but anything is possible!