IrelandXO Insight - how DNA can help you connect with Ireland

Friday, 28 February, 2020
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A frequent question on our IrelandXO Message Boards is "how can DNA help me to find out more about my Irish heritage"? It is an area that causes confusion for many people and in order to provide some concrete guidance and expert advice, we have asked Genetic Genealogist Dr Maurice Gleeson to share with us some basic information that explains what DNA testing is, and how it can help us along our journey when reconnecting with our Irish roots.

IrelandXO Insight - how DNA can help you connect with Ireland

One of the most frequent hurdles encountered by people searching for their Irish roots is that all they know about their ancestor is that he or she “came from Ireland”. And that’s it. No other information. And that makes the prospect of finding their origins and connecting with Irish relatives a daunting task. Like looking for a needle in a haystack. And that is where DNA can help. A simple DNA test can connect you with genetic cousins to whom you are related via a common ancestor. The trick is to figure out which cousins are connected to you via which ancestor. And that may be easier than you think. Genetic Genealogist Dr Maurice Gleeson shows us how DNA can help to uncover more about your Irish ancestry, and how that can help you connect with your ancestors' Irish place of origin.

There are several companies offering DNA tests to assist with your genealogical research but my favoured approach is to test initially with Ancestry (1) for two reasons:

  • They have the largest database (about 16 million people as of Jan 2020) (2)
  • You can transfer your results to other databases for free (namely MyHeritage, FamilyTreeDNA, & Gedmatch – giving you access to an additional 6 million people) (3)

The test itself is very simple – just a simple cheek swab or spitting into a small tube, and then posting it back to the lab. The results arrive 3-6 weeks later (just sign in to your online account) and consist of two components:

  1. your “Ethnicity Estimate”

  2. your List of Matches

The “Ethnicity Estimate” gives you a rough approximation of where in the world your DNA came from in the last 500-1000 years. These approximations have been getting better and better over the years as more people join the databases (and thus there are more people for comparison purposes) but also because the companies are refining the statistical algorithms they use for interrogating the data. I am particularly impressed with the estimates on Ancestry as these can now drill down to almost the county level in Ireland and (apparently) with a fair degree of accuracy. And if all you know is that your ancestor came “from Ireland”, an Ethnicity Estimate that points to counties Leitrim & Longford can be a very useful clue for focusing your research.

Figure 1: an Ethnicity Estimate from Ancestry showing hotspots in the Leitrim-Longford area and Wicklow-Carlow-Wexford area

Figure 1: an Ethnicity Estimate from Ancestry showing hotspots in the Leitrim-Longford area and Wicklow-Carlow-Wexford area

The other component of your DNA results is your List of Matches. Typically you will be presented with a list of several thousand matches – these are all genetic cousins with whom you share a common ancestor at some point in the last 250 years or so … which takes you back to approximately your 4 times great grandparents … and you have 64 of those … and it could be from any one of them.

But you don’t need to go through the entire list – I always focus on the top matches initially (say the first 10-20 matches). You may know some of them already and where they fit into your family tree. Maybe your maternal 1st cousin Doreen appears as your top match ... and this is really helpful, because any “Shared Matches” between you and Doreen must be related to you via the common ancestors you share with her, namely your maternal grandparents. And this helps focus your research on that particular ancestral line. Having several relatives tested from several ancestral lines allows you to maximise the value you get from these tests. In the ideal world, I would test four 2nd cousins – one from each of my four sets of great grandparents.

There are several tricks you can use to focus on your Irish ancestor. Let’s say your great grandparents were Thomas Ryan & Catherine O’Malley, born about 1860 “somewhere in Ireland” and they came separately to the US sometime in the 1880s, getting married in New York in 1888. Their son (your grandfather) married a woman of Japanese ancestry. Thus, the paternal side of your family is Irish and Japanese. And let’s say that your mother’s side is African and English. Since you get 50% of your DNA from each parent, and roughly 25% from each grandparent, and 12.5% from each great grandparent, it follows that about 12.5% of your matches will be from your Irish great grandfather and 12.5% from his Irish wife. This will be reflected in your Ethnicity Estimate – about 25% of your DNA will be of Irish origin, 25% Japanese origin, 25% African, and 25% English.

if your family tree has a mix of different ethnic backgrounds, this can help a lot

Figure 2: if your family tree has a mix of different ethnic backgrounds, this can help a lot

Furthermore, the Irish component of your Ethnicity Estimate may show two “hotspots” – one over Tipperary and another over Mayo. These two hotspots may indicate the area of origin of your Irish great grandparents, and consulting free online surname distribution maps (4) tells us that Ryan is more common in Tipperary and O’Malley in Mayo so that gives you a real clue as to their specific origins and where to start looking in the documentary records.

surname distribution maps (based on mid-1800 data) for the surnames Ryan (left) and O’Malley

Figure 3: surname distribution maps (based on mid-1800 data) for the surnames Ryan (left) and O’Malley (right) – from www.swilson.info/sdist.php

Turning to your list of DNA matches, you will find that many of them can easily be identified as being related to you via your Irish ancestors by using one of the following techniques:

  1. their Ethnicity Estimate is 100% Irish (i.e. no Japanese, African or English … so the connection to you has to be via your Irish great grandparents)

  2. their family tree is 100% Irish … or contains some Irish lines, but no Japanese, African or English (so the connection is not likely to be via one of your other grandparents)

Also, you find a “possible 2nd cousin” in your list of matches and in looking at her online family tree, you discover she also descends from your Irish immigrant great grandparents, Thomas Ryan & Catherine O’Malley. You start communicating but she doesn’t know where they came from either. But you click on “Shared Matches” and you get a list of your DNA matches that also appear in her list of DNA matches – the implication being that these Shared Matches are related to both you and your 2nd cousin via your Irish great grandparents (it could either be on the Ryan side or the O’Malley side).

a 2nd cousin match allows you to “triangulate” on your Irish great grandparents. Any Shared Matches are related to you either via the husband of the couple (Ryan), or the wife (O’Malley).

Figure 4: a 2nd cousin match allows you to “triangulate” on your Irish great grandparents. Any Shared Matches are related to you either via the husband of the couple (Ryan), or the wife (O’Malley).

This really helps you focus your research and with a little bit of collaboration with these Shared Matches, exchange of information, sharing of family trees, and some searching online in the documentary records (5) you stand a very good chance of breaking through your Brick Wall and identifying where in Ireland your ancestors came from, identifying who their parents and grandparents were, and connecting with Irish cousins who are still living on the same land that your ancestors left from some 140 years previously.

Welcome home!

Maurice Gleeson is a psychiatrist and pharmaceutical physician as well as a genetic genealogist. He is administrator of several Surname DNA Projects, authors several blogs, lectures on DNA worldwide, and helps people find missing ancestors (including adoptees and people of unknown parentage). He has appeared on Irish TV and is a regular contributor to genealogical magazines. His YouTube videos on genetic genealogy are particularly popular. He has organised the DNA Lectures for "Genetic Genealogy Ireland" in Dublin and Belfast since 2013 and is Education Ambassador for the International Society of Genetic Genealogy (ISOGG).

For more information about how DNA can help, visit Maurice’s website at https://dnaandfamilytreeresearch.blogspot.com and his YouTube channel at https://www.youtube.com/c/DNAandFamilyTreeResearch.  If you want to contact Maurice for a consultation, please email him: mauricegleeson AT doctors.org.uk.

Dr Maurice Gleeson Genetic Genealogist


Resources and Links mentioned in this IrelandXO Insight

  1. https://www.ancestry.com/dna/

  2. https://thednageek.com/autosomal-dna-database-growth/

  3. https://dna-explained.com/2019/04/09/dna-testing-and-transfers-whats-your-strategy/

  4. https://www.swilson.info/sdist.php

  5. There are two websites that will prove most helpful for Irish research in the 1800s - the free website www.IrishGenealogy.ie covers civil registration records (births, marriages & deaths) from 1864 onwards (1845 onwards for non-Catholic marriages); and the subscription website www.RootsIreland.ie covers church-registered baptisms and marriages, some of which can go back to the 1600s (e.g. Wexford).

  6. There are lots of educational videos available on my YouTube channel. For beginners, the following are particularly useful …


Once you have used your DNA information to find out more about your place of origin in Ireland, why not post a message on our IrelandXO Message Board and ask for guidance from our community of volunteers and members? Even if you are still in the dark about where in Ireland your ancestry lies, we can help you navigate the vast amount of resources out there and most importantly, avail of the local knowledge that is so critical in connecting people with Ireland.


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