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Surname or DNA Switch

A great blog post written by Maurice Gleeson almost a year ago calling for the term 'NPE' (Non-paternity Event or Not Parent Expected) to be referred to as Surname or DNA Switch, 'SDS'. The blog is great at explaining the possibilities and probabilities of this occurring.

For a Doherty tester born in 1950 there is 31 – 52.5% of a SDS occurring in their patriline across 37 generations to what is believed to be the surname progenitor or common ancestor of 850 – 900 AD. (continue reading for the math involved).

His probability calculations on this occurring is based on several conservative estimates from various studies of 1 – 2% per generation. Note that he calculated this incorrectly with a correction in the comments.

For Ó Dochartaigh if we are to assume that Group 1 testers descend from the progenitor of the first man to earn the title "Dochartaig" then the testers are estimated to converge at around 850-900 AD.

If we have a male Doherty (or variant spelling) tester born around 1950 then, on average assuming 30 years per generation, there would be approximately 1,100 years to this progenitor or ~37 generations.

So, the calculation for a 1% per generation would be:

0.99 ^ 37 = 0.6894

which is stating there is a 68.9% chance this Doherty tester DID NOT HAVE AN SDS on his line, or, in other terms, there is a 31% chance this tester's patriline experienced an SDS.

Same calculation for 2% would be:

0.98 ^ 37 = 0.4735 or 47.4% of no SDS, in other terms 52.6% probability of a SDS occurring across 37 generations.

So, a male tester born in 1950 would have a 31 – 52.5% chance of a Surname or DNA Switch on their patriline across 37 generations or approximately back to 850 AD when Group 1 Dohertys converge on a common ancestor. Please keep in mind regardless of this happening on one's patriline it should not diminish your identity as a Doherty. If you are born a Doherty then you are a Doherty, plain and simple.

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Zack Daugherty
Zack Daugherty
17 juin 2019

Yes, the DF97+ but BY471- clade (your clade) is one that I'd estimate is pretty old (estimated by the width of testers so far) and very close to whomever the BY471 ancestor was obviously descending from the same recent ancestors as the BY471 fellow would have been. I think it is important for everyone to know that BY471 ancestor is quite likely NOT the progenitor of the surname, but simply that it was likely close to this individual and contains the largest concentration of Doherty testers and Septs historically believed to be off-shoots of a Doherty ancestor. Even if one is not positive for BY471 or even its father clade DF97...even if they are haplogroup I, J, E, etc. it still should…


Will Dougherty III
Will Dougherty III
17 juin 2019

Wow, Zack, I didn't realize the probability that someones name or DNA were switched was that high, but when you do the math, it begins to make sense. In the back of my mind I always knew it was a possibility, but always hoped it wasn't in my line. When I finally took a DNA test I was relieved that I had a Doherty/Dougherty match in New Zealand. My Y-DNA match was from New Zealand and his Dohertys came from Derry via England and India. I knew at that time that my (US) Doughertys had been here for at least two centuries and were supposed to have came from Ireland also, so I figured I was ok. What I didn't…

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