Saturday, May 5, 2012

Genetic genealogy journey - FamilyTreeDNA Y-DNA Test - Part 2

On 23 April I posted Expect the unexpected in which I described my first steps into the world of genetic genealogy. To summarise, my reasons for taking the first steps into genetic genealogy were:

To find out whether my direct paternal line (father's father's father...) descends from the O'Brien clan (Irish Type III, descendants of the Dalcassian sept) or whether they are part of another Irish clan such as the Byrnes.

My direct paternal line originated in the north of Ireland, so I did suspect that perhaps we were not related to the O'Brien's who are mostly associated with County Clare and surrounding counties. My suspicions have been confirmed.

I received an email from FamilyTreeDNA two days ago informing me that my Dad's 37 marker results had been posted to the site. At 37 markers Dad had no exact matches (37/37), no matches with a genetic distance of 1 (36/37) and no matches with a genetic distance 2 (35/37). However, there were two matches with a genetic distance of 3 (34/37) and two matches with a genetic distance of 4 (33/37) (See FamilyTreeDNA: Interpreting Genetic Distance Within Surname Project for more information about genetic distance).

One match with a similar name and place of origin was expected as this match had also appeared at 12 and 25 markers. I have sent an email to that person.

It seems my direct paternal line were neither part of the O'Brien clan nor the Byrne clan. For a while (a day?) I felt a little disappointed with these results as I had hoped to find we belonged to one of the groups within either of these surname projects. However, I have decided this unexpected result is good because now the person who submitted the other test (the one with the similar name and origins) has a match! There is about a 50 per cent chance that my Dad and this other person shared a common ancestor within 9 generations (not less than 6 generations when you take into account the information I already know about the direct paternal line from 'paper trail' research), and about a 90 per cent chance that they shared a common ancestor within 16 generations. These same odds also relate to the other person whom Dad matched 34/37 - that person had a different non-Irish surname (a surname which also occurred within the two 33/37 matches).

I was a little disappointed that there were not more results, but I guess this is because the number of people who have taken the first steps in genetic genealogy is still fairly limited.

The other disappointment was that I somehow felt a little less Irish than I had felt before. However, I realise this is just one branch of my tree. Sixteen generations ago Dad had 65,536 ancestors = 32,768 male ancestors (see the web site Number of Ancestors in a Given Generation and Dick Eastman's Genealogy Newsletter How Many Ancestors Do You Have?). So the most recent common ancestor between Dad and these matches is 90 per cent likely to have been just one of these 32,768 male ancestors. Some of these ancestors would surely have been the same people (see and the Wikipedia article Pedigree Collapse).

So, how useful and informative is a Y-DNA test? It is useful for surname projects and useful for proving a relationship between two individuals along the direct paternal line (I can think of a few other Irish branches of my tree where this would be very useful in proving a connection back in Ireland). However, you need to keep in mind that a Y-DNA test is ofcourse limited as it can only tell you about one branch of your family tree (your father's father's father's father's branch).

Creative Commons License Australian Genealogy Journeys by Aillin O'Brien is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Australia License.Permissions beyond the scope of this license may be available at Clipart from Open Clip Art Library


  1. For a long time I wasn't keen to go down the DNA route but lately I've been giving it some serious thought. I'd really like to be able to test my O'Brien links too but not sure who would fit the line...will have to look at it more closely. I'd have liked my dad to be tested but there wouldn't have been a chance he'd do it, but irrelevant as he's no longer with us. Look forward to hearing your feedback on the linked families.

    1. Thanks Pauleen. I think there is lots of potential in the use of DNA for Irish research particularly. As I mentioned in my post I think there are a few other Irish branches of my tree where this could be useful (e.g. another family where I think the name was changed between Ireland and Australia).
      Your O'Brien's would probably be of Irish Type III haplotype as they come from County Clare. It is a bit of an irony that it appears I am probably more closely related to the O'Brien clan through my Hehir and McMahon ancestors! Very interesting so far, even if not quite what I expected :)


Your comments are appreciated. Thanks.

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