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Testing cousins to filter your family tree

Many of us have taken a DNA test to advance our family history research. Some people have been able to go further and test parents too. But have you considered testing your parents’ cousins? This was something I did right from the start, as my budget allowed. My mother’s lovely cousin, sadly no longer with us, tested herself on Ancestry and just appeared in my match list one day. I knew this cousin well so could immediately place her. As I looked at our shared matches, it dawned on me that everyone she and I matched would be related on that quarter of my family tree. They’d all be connected in some way to my maternal grandmother’s family. Knowing that automatically ruled out 3/4 of my ancestors allowing me to focus in on that branch when trying to figure out matches. Some of my mother’s paternal cousins have subsequently tested on a variety of sites & it’s allowed me to do the same exercise for that branch.

On my paternal lines, there were far fewer choices. Dad actually only has 7 first cousins (coming from just 3 families), which is a tiny amount for an Irish person born in the 1950s. Two of those cousins are not really in contact with the family, although I do know where they are. So I asked two of the remaining 5 that I knew best to take a test for me, one on each side, at my expense. Happily both agreed. However, that was several years ago, and before Ancestry hit the market in Ireland, so they’re on the now relatively small database of FamilyTree DNA.

My one major brick wall in my ancestry is my 2x great-grandparents, Thomas Reilly & Elizabeth Murphy, my paternal grandmother’s grandparents. I talked about them on the Family Histories podcast in 2022. There’s no record of their marriage and they had just one child (born in 1882) who lived to adulthood, so while there must be DNA cousins for this branch, they are complete unknowns to me. For a long time, I’ve been working on a large paternal cluster of connected DNA matches across all the databases. Some of the people in the cluster match my aunt, uncle and 1C1R at high levels (e.g. 150 centimorgans, which should be a figurable-out relationship). I’ve traced the family trees of these 15 people but can find no links to my own genealogy. There is a location match to my paternal grandfather’s mother’s family, but here the cousins came in useful. These people do not match my Dad’s paternal first cousin, they match his MATERNAL first cousin. So I’ve known for a while that this cluster must link to my paternal grandmother’s branch.

I recently asked that same cousin to test on Ancestry, which now has over 25 million people in their database, in the hope that the larger numbers might help with the brickwall. His results came in at the weekend and one thing has already become clear: I’ve narrowed the mystery cluster to my grandmother’s father’s side! There were some known relatives to my grandmother’s maternal line, the Longs, already in the database there, but now I can compare them to an earlier generation than me. There’s no overlap at all between these people and the mystery cluster. I couldn’t compare before because the Long matches are not on MyHeritage or FTDNA, and the matches to me are small, so I can’t rely on individual ones. There is a lot more work to do before I can crack this case but there’s a chink in the wall now.

If you’d like some help with a brick wall, please get in touch!

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