Page 8 - O Mahony Journal 2025

you will soon hear – his ability to correctly pronounce Irish names and places (a talent
I have not yet acquired). I also miss his sense of humor and his gentle tolerance for
my many questions. He was a very fine gentleman.

In laying additional foundation for the presentation, John reviewed some history known to some
but always worth reviewing: How did the O Mahony name originate?

The O Mahony’s are named after Mahon (Mathghamahna), Chief of the Eóganacht Raithlind,
who died sometime around 1038. Mahon was the son of Cian, who led Brian Boru’s 2nd
Division at the Battle of Clontarf. Mahon’s mother was Sadhbh, daughter of Brian Boru.

At that time, the name Mahon was a common given name or forename so that there
could be many O Mahony families named after a Mahon that are not related to Mahon
mac Cian. For example, Brian Boru’s elder brother was named Mahon and is believed
to be the ancestor of the MacMahon clan. So the common use of the Mahon given
name may be one reason among many that may account for the diversity of family
lineages we see in the Y-DNA project. Other explanations include: the welcoming
nature of the tribal community at that time, an NPE [Ed. Note: Non Paternal Event],
adoptions, men taking their wife’s surname, name changes to further a rise to notoriety,
or as Finbar once said to me about my ancestors, some people changed their name
to help hide from the law.

John knew first-hand that the language of genetic genealogy can be daunting at first, and he provide
a glossary of commonly used terms.

What is a Genetic Marker?

A marker (largely synonymous with the word “landmark” and often referred to as a
genomic marker or a genetic marker) is a DNA sequence, typically with a known
location in a genome. Markers can reflect random sequences, genomic variants,
or genes.

• Haplotype
A haplotype is a set of genetic markers inherited together from one parent.
Two individuals that match exactly on all markers have the same haplotype.

• Haplogroup
A haplogroup is a major branch on either the maternal or paternal tree of humankind.
Haplogroups are associated with early human migrations. Today, these can be
associated with a geographic region or regions. Example: R1b-M343 is the most
common Y haplogroup of men across Europe and the Americas. Example: mtDNA
haplogroup H can be found within as much as 40% of European people, making it
the most common maternal haplogroup in the West.
Note: The letter names of the haplogroups run from A to Z and were named in order of
discovery. The letters do not have any meaning in terms of genetic relationships. There
are two kinds of haplogroups: the paternally inherited Y-chromosome DNA (Y-DNA)
haplogroups, and the maternally inherited mitochondrial DNA (mtDNA) haplogroups.
They respectively indicate the agnatic (or patrilineal) and cognatic (or matrilineal)
ancestry. Though maternal and paternal haplogroups may have similar naming

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