Did You Know? DNA Can Offer Clues about Irish Ancestry.

Nearly 37 million Americans claim to have Irish heritage according to a national survey conducted in 2009. That’s over eight times the number of people living in Ireland today. Although it’s remarkable that nearly 1 in 10 Americans might say “Kiss Me I’m Irish!” on St. Patrick’s day, it’s not clear if all these people actually have Irish ancestors or if they simply feel an affinity for corned beef and green beer.

So how do you know if you have Irish ancestry? Often this information is passed down through family stories, for instance my mother claims to be a quarter Irish and so I’m apparently one-eighth Irish. But can I look at my DNA to verify this?

It turns out that maternal and paternal lines can offer some clues about Irish ancestry. In my case, my maternal line, traced through mitochondrial DNA that I inherited from my mother (thanks Mom!), told me that I’m a sub-type of a lineage called H6a (specifically H6a1b). H6a is is an offshoot of the broader H maternal line and is found at low levels — 4% or less — in the Czech Republic, Slovakia, France, Sweden… and Ireland! So, although it doesn’t completely verify the story, this one branch of my ancestral tree is at least consistent with claims of Irish ancestry on my mother’s side.

What is a “maternal line”?
Maternal lines are inherited through mitochondrial DNA — both women and men have mitochondrial DNA, but it’s only the mother’s mitochondrial DNA that is passed on to a child.

What is a “paternal line”?
Paternal lines are inherited through the Y chromosome, which only men have. (Remember that women have two X chromosomes while men have one X and one Y chromosome). Since women don’t inherit a Y chromosome, they must trace their paternal line through their father’s, brother’s or paternal uncle’s Y-chromosome data.

If instead I want to see if I have Irish ancestry on my father’s side (even though my father has never claimed to be Irish!), I can investigate my paternal line, which is traced through DNA on the Y chromosome and passed from father to son. Even though I don’t have a Y chromosome, I can learn about my paternal line through my biological brother’s or father’s DNA.

85% of Irish men belong to a paternal lineage called R1b1b2, but since this line is also common across the rest of western Europe, it doesn’t definitively determine if a man has Irish ancestry. If a man has a sub-type of this lineage (called R1b1b2a1a2f2), however, it’s much more likely that his DNA might actually trace to Ireland. Research suggests that many men of this line are descendants of an Irish king named “Niall of the Nine Hostages” who ruled during the 4th and 5th centuries. According to legend, Niall led one of the most powerful and enduring Irish kingdoms and it has been suggested that because of high rates of Irish emigration to North America and other parts of the world, up to two or three million men descend from Niall!

Learning about our ancestry is particularly fun when we can toast to it. Even if you don’t have Irish ancestry, we wish you a Happy St. Patrick’s day and encourage you to explore the hidden stories in your DNA.

(23andMe customers can also learn more about their ancestry with our Relative Finder feature, which helps customers connect and compare their DNA, and with Ancestry Finder, a lab that maps your DNA to potential countries of origin. Not a member? Visit our store or set up a free trial account to learn more.)

Did you know? provides tidbits of information about genetics (both in humans and in other animals) and explains how DNA relates to both ancestry and health.






  • Curtis bianco

    I would like to what Ethnicities of white I have in me weather Im Italian Irish Scottish English welsh Native American of Jews or African or Asian. What DNA sample can Provide that

    • BethannH

      Hello Curtis,
      23andMe has recently updated its main ancestry feature and now provides even more information about where you come from. This new feature is called “Ancestry Composition.” You can find out if you have ancestry from Northern, Southern, or Eastern Europe. If you have ancestry from Scandinavia or the British Isles or Ireland you can find that out, too. This new feature also provides more information about ancestry from Africa, Asia, and can differentiate Native American ancestry from Asian ancestry. To build this feature, 23andMe used DNA from people from different parts of the world to build a “reference” population. 23andMe then compares your DNA to this reference population. Check out all of our ancestry features here: https://www.23andme.com/ancestry/

      Here is also a link to a review of current ancestry services on the market: http://www.yourgeneticgenealogist.com/2012/12/comparing-admixture-test-results-across.html

  • ?? Tina Hunter

    I just wanted to say that I too am H6a1b. Interesting post

  • http://www.texirish.org MJ Triola

    My cousin took a y-DNA test for our paternal Irish line and I took an mt-DNA test for our maternal Irish line, but the results are too broad to identify a specific province, county, or parish in Ireland. Despite the fact that we have assumed that the Barry side of our family was Anglo-Norman, my cousin’s profile is very close to Irish Type III also known as Western Atlantic Modal Type which would be primarily Gaelic. Has 23andMe started to develop reference samples within the “British Isles and Ireland” that can separate Gaelic from Anglo-Norman from Ulster Scot from mainland British? I’ve read news articles about 2 past genetic surveys of Ireland by scientific groups. Are the results of these surveys available to 23andMe?

    • BethannH

      Thank you for your comment. 23andMe has not developed reference samples from the British Isles and Ireland in order to provide the type of information you are seeking. It’s possible that we could look into developing such a feature in the future, though.

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