What we Don't Have in Common

 

Perhaps in wrestling with a research problem, we struggle so much that we end up on the far side of reasonable conclusions. Perhaps, after comparing and contrasting DNA matches over and over today, I've reached that far end. But the thought this day left me with might have some validity, despite the mental exhaustion. I'm wondering whether it might be far more productive for me to partner with Flanagan cousins whose matches have nothing in common with my family, as far as DNA goes. What we don't have in common may provide the answer we seek.

I'm searching for DNA matches who share genetic material with my husband and a common heritage in County Limerick with his Flanagan ancestors. Other than close relatives descended from the very same second great-grandmother as my husband claims—Anna Flanagan—I've found very little to work with. If I search for DNA matches whose family tree includes Flanagan surnames, I end up with matches whose ancestors hailed from County Cork, or even County Mayo, not County Limerick.

Trying to find DNA matches with another descendant of a second great-grandparent would mean finding a third cousin, at the closest. At that point, it is quite possible that two such cousins would share absolutely no genetic material in common, despite both being descended from the same ancestral couple. In other words, the shared centiMorgans might amount to an absolute zero.

If what I am actually trying to accomplish is to push back even beyond that second great-grandmother, it would mean finding descendants of a third great-grandparent, thus looking for fourth cousins. At that level, it would be even less likely to find someone who shares the same Flanagan genetic signature as my husband.

In other words, the more distant the relationship, the less likely that two such cousins would share any genetic material at all. 

But what genetic Flanagan signature my husband might not share with his own DNA matches could very well be the exact segment that a Flanagan cousin might share with a different family member. In other words, rather than reading the ProTools results for cousins who share DNA with my husband's test and a match in common, I need to find the matches of our matches who share different Flanagan DNA segments with their own matches—not in common with my test, but in common with other Flanagan cousins.

While that might sound reasonable in theory, in practice, it would take cooperation between cousins who are willing to share their data. Perhaps a letter writing campaign might convince candidates to join up to solve this Flanagan mystery. On the other hand, at a third cousin level, the greatest amount of genetic material any one match set could share would be 234 centiMorgans—a small amount, indeed, but also an amount which shows us how much variability there is between what one third cousin could inherit versus another third cousin descended from the same second great-grandmother.

In other words, I'm looking for someone with DNA in common with my husband's Flanagan ancestor who has other Flanagan matches who do not share the Flanagan segments that match shares with my husband. Perhaps there's someone out there who inherited all the Flanagan genes that my husband did not. I hope that person took a DNA test and posted the results, along with a complete family tree. At least, I can dream.