I. What the clan is doing

A shared project, decades in the making. For generations, members of this clan have tried to piece together who we are and where we came from — through parish registers, census rolls, gravestones, and the annals of Mac Fhirbhisigh. DNA is the newest tool in that same long effort. It does not replace the paper record; it tests it.

At the 2022 Gathering, the clan's Genealogy Committee presented its first report on DNA. Four years later, the landscape has changed — the databases are larger, the science is sharper, and one of the three big testing companies has changed hands. This page, and the three that sit beneath it, bring that work up to date.

II. Why DNA matters for this clan

The question is dynastic. The O'Dubhda trace their descent from Fiachra mac Echdach Muigmedón, brother of Niall of the Nine Hostages — in the fourth century AD. No written source can prove that line unbroken. But the Y chromosome, which passes father to son with only tiny, measurable mutations, carries a signal that can be read across sixteen centuries.

Recent deep-SNP testing has identified a specific Y-chromosome signature — R-FGC23742 — that researchers now associate with the Uí Fiachrach kindred. If enough O'Dubhda men test into this branch, we can say, with genetic evidence, that our family tradition is borne out by the chromosomes we carry. That is a contribution not only to our own clan but to Irish history at large.

III. The three kinds of test

Any conversation about DNA testing has to begin with the three different kinds of test you can take. Each tells a different story — and the story you are after determines which test (and which company) you need.

• Y-DNA — passed father to son, essentially unchanged. Only males can test. Traces the direct paternal line back thousands of years. This is the test that speaks to the Fiachra question.
• Mitochondrial DNA (mtDNA) — passed mother to child, essentially unchanged. Everyone has it; only women pass it on. Traces the direct maternal line.
• Autosomal DNA — a reshuffled mix inherited from all your ancestors for the last five to eight generations. This is what Ancestry, 23andMe and MyHeritage use for ethnicity estimates and living-cousin matches.

A fuller explanation, with examples of the kind of question each test can answer, is in Understanding DNA Tests.

IV. DNA and the Septs

A future direction. The septs of the clan — currently documented at Bonniconlon, Dublin, Kerry, and Mayo — are kinship groupings drawn from the paper record. DNA cannot replace that record. But it can test it: confirming where branches truly connect, and occasionally revealing connections the paper never knew about.

The clan's long-term aim is to pair each documented sept with a Y-DNA fingerprint — so that a man bearing the O'Dubhda surname, anywhere in the world, could one day test and find not only that he is of this clan but which branch he springs from. That work depends on volunteers. If you have tested already, or would like to, please write to us.

V. Where to go from here

Three pages sit beneath this one. Start with whichever answers your question first:

• Understanding DNA Tests — if you are new to this and want the plain-English version.
• The Y-DNA Project — the dynastic question, the Uí Fiachrach signature, and how to join the research.
• How to Test — which company, which kit, and what to do if you've already tested somewhere.

Popular accounts of Irish DNA still equate the R-M222 marker with "Niall of the Nine Hostages." In fact, M222 is older and broader — it is the signature of a group of related dynasties, including the Uí Néill, the Uí Briúin, and our own Uí Fiachrach.

The more refined Uí Fiachrach branch, R-FGC23742, has only emerged in the last few years of Big Y testing. This clan is in a position to help refine that picture — which is the project this page invites you to join.

— Genealogy Committee

If you have Y-DNA tested at FamilyTreeDNA, consider joining these projects (all free):

• Dowd Surname Project
• Sons of Aodh (Uí Fiachrach)
• Ireland yDNA
• R-M222 & Subclades