An open letter to my DNA cousins

Dear Cousin,

I’m so glad to ‘meet’ you through DNA testing! I have lots of family history gems to share and explore with you. Perhaps we can help each other. I have copies of wills and obituaries and photos and maps I can send you–and family lore too!

Since March is the month we celebrate St. Patrick’s Day, I thought I’d offer several Irish examples. (But there’s a Colonial American example at the end too.)


Let’s start with a chain migration story! Teenage Mary Melville left Ireland for the U.S. around 1880 and, like so many others, hired on as a domestic servant. Perhaps she sent some of her meager pay home; within two or three years, her sisters Ellen and Jennie were able to  follow her. All of them settled in the Corktown area of Detroit. The youngest sibling, their half-brother John, boarded a ship by himself in 1885 and made his way to America, where he moved in with his married sister Jennie and found employment as a clerk. I’d always wondered why a 16-year-old boy made that long journey across the Atlantic Ocean by himself. DNA led me to discover these sisters.

Or here’s a chain migration that didn’t happen! My great-aunt told me her Grandfather Mike allegedly left a wife and children in Ireland to come to America, planning to save up and send for them… but instead fell in love with a girl named Bridget and started a new family here with her! DNA may one day help us figure out the truth.

There are stories of triumph, like my ancestor whose invention secured him a US patent and made his fortune… And there are tragedies, like the farmer who fell from his hayloft, landed on a pitchfork, and died young, leaving a widow with five children. If these Irish immigrant families are your kin too, I’m happy to send you more details!

Communicating with our genetic matches helps us to share and preserve our stories. It can also help us to investigate our mysteries.

I’m half-Irish on my dad’s side and half-Irish on my mom’s. Of my 16 great-great-grandparents, eight left Ireland between 1840 and 1885, and I suspect they came from seven or eight different counties. DNA is my best hope for discovering what counties or villages they may have come from.

Image 1. Where did our Irish ancestors come from?

Mar 2018 Ireland

By Population_density_of_Ireland_map2002.svg:  via Wikimedia Commons

Consider my great-great-granddad James Flynn. He was born *somewhere* in Ireland, apparently sometime between 1836 and 1842. There were probably a LOT of babies named James Flynn born in Ireland in that period. None of my research in North American sources has helped me narrow down a birthplace. But DNA might.

Of course, it’s not enough to be a DNA match to someone (let’s call him Cousin Hugh) with a Flynn in his family tree born in the 1830s in, say, County Leitrim. After all, I have eight different lines from Ireland; our common ancestor could be someone a generation or more farther back, on a completely different line, with a surname neither has discovered yet.

But here is how genetic cousins can help each other. Say a New Cousin matches me or my siblings. Any one or more of the following may also be true.

  • If New Cousin matches my aunt, uncle or 1st cousin (esp. if on the same section of the same chromosome where I match them), then I’m pretty sure which pair of my grandparents passed me that segment of DNA that matches New Cousin. Our common ancestor will come from that 1/2 of my family tree.
  • Likewise, if he/she matches my 1st cousin once removed or 2nd cousin…. I’m pretty sure our common ancestor will come from that 1/4th of my family tree.
  • Likewise, if he/she matches my 2nd cousin once removed or 3nd cousin…. I’m pretty sure our common ancestor will come from that 1/8th of my family tree.
  • Likewise, if he/she matches my 3rd cousin once removed or 4th cousin…. I’m pretty sure our common ancestor will come from that 1/16th of my family tree.

So, remember hypothetical genetic cousin Hugh, whose tree has an Edward Flynn from County Leitrim, born around the same time as my paternal ancestor James Flynn? I want to know if Hugh matches any of my 2nd, 3rd, or 4th cousins that also descend from my James Flynn. If Hugh does, then that makes a stronger case for a hypothesis that my James Flynn might be his Edward’s brother or close cousin, and James may be from County Leitrim, Ireland, too. If, instead, we find that Hugh matches one of my cousins descended from my maternal ancestor Michael Cahill, then the fact that Hugh has a Flynn in his tree is irrelevant. His Flynns are probably not related to my Flynns.

The same process applies to my non-Irish ancestors, where I’m looking for parents and not just birthplace. If genetic cousin Sue has an ancestor James Jennings around the same age as my ancestor Elizabeth Jennings, and they live next door, can I assume that James and Lizzie are siblings and share the same father? I wish it did, because I don’t know Lizzie’s father, but we can identify James’s father.

That one DNA match isn’t proof, but what if Sue matches not only me or my siblings but also my 2nd, 3rd, or 4th cousins that descend from Lizzie? If we all have the same piece of DNA on the same chromosome (i.e. each of us matches each other, one-to-one, on the same segment), it’s called triangulation and is even more convincing evidence that we share the same individual ancestor. See image 2. For more information on triangulation, see my March 2017 blog post here.

Image 2.

Mar 2018 blog

Image 2 shows what I know so far of my DNA matches on the  chromosome 11 I got from my mom. You can see a segment where I match my 1st cousin once removed (1c1r), and third cousin (3c), and fourth cousin (4c), all of whom descend from Lizzie Jennings. We all match each other in that area of that chromosome, and Sue matches each of us there too! We likely have the same person in all our family trees: it seems more plausible now that James and Lizzie Jennings are related.

Dear 2nd, 3rd, and 4th cousins—we probably all have a genealogy brick wall in common. If you participate in this effort to compare our DNA to each other, your family tree can benefit too!

Just one problem though…

We’re trying to work with a network of cousins, but what if one of these cousins tested at AncestryDNA and another at MyHeritage and another at FamilyTreeDNA and another at 23andMe. How can we find out if/how we match each other?

Happily, there is a solution: GEDmatch lets DNA testers see if/how they match each other, for free, regardless of which of those four companies they tested with. (*) So if we are DNA cousins, I hope you will consider copying your raw DNA data to GEDmatch. Many websites offer instructions, but some have more current details than others. For example, genealogy blogger Mags Gaulden has helpful instructions at Grandma’s Genes, “DNA raw data to GEDmatch,” posted 7 Nov 2017.

Once your data is on GEDmatch, I’ll try to figure out where our DNA cousins connect with us and how far back we can take our family trees. I’ll let you know what I find out, and I’ll send you copies of photos or stories or maps or documents about our common ancestors too, if you’re interested.

If you’re a DNA match to me or my family and you’re willing to try GEDmatch but need a hand with this step, email me at I’m happy to assist with your DNA, and I can help you set up a public or private family tree too if you want. And if you’d like some coaching on how to use the tools at GEDmatch yourself, I can do that as well. After all, we’re kin!

Happy St. Patrick’s Day, and I hope you’ll get in touch with me soon, if you have questions or if you’re willing to help.

Sláinte! (to all!)

Ann Raymont © 2018

(*) GEDmatch caveat: DNA kits processed by 23andMe as of August 2017 are not compatible with regular GEDmatch and may not transfer there. GEDmatch Genesis is being beta-tested to support that chip, as well as to support folks who tested at LivingDNA, but it isn’t fully functional yet.



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