Page 18 - O Mahony Journal 2025

Hostages, King of Tara, but that belief is now being questioned. However, the M222 SNP is very
common in Northern Ireland and Scotland.
The two men in this group are very closely related and share a common ancestor around
1800. Both of our two members know their earliest known ancestors were from western
Ireland (Bantry and Crookhaven), and for one member, there is a strong family tradition that
his paternal ancestor was known as O Mahony Finn. Thus, this group may be part of the O
Mahony Finn sept that was part of the Western O Mahony homelands.

• FGC5494
The last group to be highlighted today is the FGC5494 cluster. It does not have a “type”
designation and was only identified in 2014. There are 25 members in this cluster, with five
members (or 20%) who have taken a Big Y test. FGC5494 has a broad distribution throughout
Ireland and the European continent, and it is difficult to associate this haplogroup with any
historical O Mahony homeland or tribal chief. If one maps known locations for the earliest
ancestors for the members of this cluster, you find locations spread throughout the traditional
O Mahony homelands from Cork to the Mizzen Head Peninsula as well as Northern Ireland
and Belgium. As more members join or upgrade to higher marker tests, a clearer picture for
this group should emerge.

As of May 2023, the O’Mahony Society DNA project includes Y-DNA results for 203
individuals. 97% of O Mahony Y-DNA testers are members of the R haplogroup. Throughout
Ireland, haplogroup R membership is approximately 81%.

Y-DNA Haplogroups – distribution -
R Haplogroup : 195
E Haplogroup : 3
N Haplogroup : 1
I Haplogroup: 4

There are 32 Y-DNA subgroups, and of these subgroups, the following
identified/named clusters appear:
Irish Type I (M222 SNP) 2 testers
Irish Type II (CTS4466 SNP) 74 testers
Irish Type III (L226 SNP) 17 testers
FGC5494 SNP 25 testers

In conclusion, when it comes to genetic genealogy, autosomal, Y-DNA and mt-DNA
all have a role. For the future of the Y-DNA Surname Project, as more people join,
more SNPs are identified, and more people test STRs at a higher level, the project
data will become more refined with a greater understanding of our relationships to
each other and the history of the O Mahony clan.

John, we didn’t know you long enough, but your genius lives on. Thank you, thank you, thank you all.

Acknowledgements:
• Many thanks for the work and dedication of Dr. Finbar O Mahony in his support of the Y-DNA Project.
• Gwynneth O’Mahony Bennet - O Mahony Society 2023 Journal: “O’Mahony by Name: Dalcassian by Decent”.
• The O’Mahonys: A multi-disciplinary approach to a genetic surname study. Cai Maver, 2017 May 30.
http://caimaver.com/mahoney/dna-paper/the-omahonys-paper_maver_2017.pdf
• International Society of Genetic Genealogists https://isogg.org/

18