top of page













Project Background


The O Mahony Genetic Genealogy Project, formerly known as The O Mahony Surname DNA project, was begun on 1 August 2003 by Perry Streeter and was transferred in early 2007 to the O Mahony Society for ongoing administration.  It is currently administered by  Patrick O Mahony and Tom Weingart (adding his expertise in mitochondrial DNA ).  


The project's typical Y-DNA participant is a person whose patrilineal ancestry (father’s line) traces back as an O Mahony (or a variant surname) each generation going back in time.  By contrast, the project's typical mtDNA participant is someone whose earliest known matrilineal ancestor (mother’s line) is an O Mahony (or a variant surname).  Per genealogical research terms this matrilineal ancestor in many cases will be considered the "brick wall" ancestor.  However, knowing the mtDNA of the matrilineal ancestor may lead one to connect with that ancestor's maternal family - for example, the family of that ancestor's mother or sister.   


Geneticists can now study the Y-chromosome DNA of males bearing all variations of the

O Mahony surname to determine whether or not they are related, and the approximate degree of their kinship.  For an excellent explanation of this process, please see DNA 101 at the BLAIR DNA Project.


The project uses the services of the reputable DNA testing company,  Family Tree DNA, and through them we are creating a specific O Mahony Surname DNA database. To address any concerns that you may have about privacy, please click here. To collect a DNA sample, a simple, painless cheek-scraping test is used instead of a blood test. View a video of cheek swabbing process.


A word of caution:  DNA testing can also reveal unexpected evidence adoption, maternal infidelity, ancient fostering leading to a name change, a name change to allow inheritance of the family-owned land, etc. These events could have occurred anywhere in a lineage right back to the time of the adoption of surnames or even before.  Consequently, any O Mahony male who tests his DNA should be prepared for the small possibility that he may not find many O Mahony matches or may match families other than O Mahony. 


Project Objectives

  • Identify how many distinct O Mahony family lines originated in Ireland.

  • Determine whether or not O Mahony Irish emigrants to a given country were related to each other.

  • Enable a living male O Mahony anywhere in the world to possibly identify his family’s O Mahony sept/branch of origin.


We are especially seeking participants who are descendants of the O Mahony Clan's major septs/branches.  If you have credible family lore and/or documentation linking to one of them, financial assistance may be available.  Please email  Patrick O Mahoney or Tom Weingart for more information.



                                                    JOIN THE PROJECT TODAY TO SEE YOUR ANCESTOR REPRESENTED!

For Your Viewing Pleasure--A Little More Background

Thanks to YouTube, we can hear Emeritus Project Administrator and former Taoiseach Finbar O Mahony's 2013 presentation to the Royal Dublin Society on the O Mahonys:  our society, our heritage, and our O Mahony Surname yDNA Project.



om-dna copy (002).jpg
HD Crest 300 2020.png
bottom of page