the o’mahonys - cai mavercaimaver.com/mahoney/dna-paper/the-omahonys-paper_maver_2017.pdf · the...

The O’Mahonys A multi-disciplinary approach to a genetic surname study

Cai Maver, [email protected], 2017 May 30

Abstract The O’Mahonys are an Irish family who claim descent from Mahon, son of Cian, who lived in the 11th

century AD and became chief of the Eóganacht Raithlind tribe of south Munster. The O’Mahony family is

conspicuous in the historical record, with many named septs associated with specific lands in counties

Cork and Kerry. This paper examines the genetic and geographic data of participants in the O’Mahony

Surname Project to determine if any of the genetically distinct families bearing the surname can be

connected to any particular person, sept, or lineage in the historical record. In doing so, this paper

attempts to suggest which haplogroup the progenitor of the clan, Mahon, might have belonged to.

Background

The Historical Record The O’Mahonys are reputedly descendants of Corc, King of Munster, who lived in the fifth century AD

(O’Hart, 1892; O’Mahony, 1913). Aside from the O’Mahonys, Corc is said to be the ancestor of all of the

Eoghanacht clans who would become families such as the O’Sullivans, the MacCarthys, the

O’Donoghues and the Stuarts of Scotland. However, we can’t assume that an ancestor’s surname

indicates direct, patrilineal descent from a single common ancestor – in this early age, families might

adopt the name of a famous ancestor regardless of whether that ancestor was on the mother’s or

father’s side (O’Mahony, 1913). In examining the O’Mahonys, or any surname group, it is necessary to

limit the investigation to the time period when surnames were passed down in a patrilineal manner.

The O’Mahonys are named after Mahon (Mathghamhna in Irish), chief of the Eóganacht Raithlind tribe

who died in 1038AD (O’Mahony, 1913). Mahon was the son of Cian, who lead Brian Boru’s second

division at the Battle of Clontarf, and Sadhbh, a daughter of Brian Boru (O’Mahony, 1913). In this time

period, Mahon was a given name, and we should expect that there will be other lineages who are

descendants of a man named Mahon (thus MacMahon or O’Mahony), but who are not descendants of

Mahon son of Cian (Mahon mac Cian). For example, Sadhbh’s uncle, Brian’s elder brother, was also

named Mahon and he is said to be the ancestor of the MacMahon’s (O’Hart, 1892).

Cian’s 4x great-grandson Donogh na Himerce Tiomcuil O’Mahony is, according to the histories, the most

recent common ancestor for all the O’Mahonys who descend from Cian (O’Mahony, 1913). Donogh was

the last chief of the united O’Mahonys; upon his death in 1212AD, his son Diarmuid Mor O’Mahony

became the chief of the western O’Mahonys based around the Mizen Peninsula while his son Concobar

became chief of the O’Mahonys of Kinelmeky. Septs – named lineages of the family descended from a

significant ancestor and usually associated with a geographic area – descend from either Diarmuid Mor

mailto:[email protected]

The O’Mahonys: A multi-disciplinary approach to a genetic surname study 2

or Concobar, and the lands occupied by these septs may reveal clues regarding from which branch of

the family they descend.

The descendants of Diarmuid Mor and Concobar are fairly well documented and outlined in Rev. John

O’Mahony’s comprehensive History of the O’Mahony Septs of Kinelmeky and Ivagha (1913), but the sons

of many of the minor septs are not often given in the sources used by O’Mahony. The history on most

lines goes to the 1600s when many of the O’Mahony lands were lost and many of the clan left for the

continent. There is a roughly 100 year period from the late 1600s to the early 1800s – corresponding

with the time of the Catholic Penal Laws in Ireland – when there are very few records of the family.

Like many families of Irish heritage, today’s O’Mahonys are generally able to trace their ancestors back

to the 1800s, though often with great difficulty. The 19th century Irish diaspora spread the O’Mahony

kinsmen around the globe, and not all are able to determine where in Ireland their O’Mahony ancestors

came from. We turn to genetics to try and bridge the gap from our modern family tree back to that of

Mahon mac Cian.

The Genetic Record The O’Mahony Surname Project (2017) has been collecting and organizing genetic data from

descendants of many O’Mahony families (and families with variants of the surname) since 2003, and

much of that data has been published online. Nearly all of the members in the O’Mahony Surname

Project descend from a common paternal ancestor by virtue of the fact that they share the L21 Single

Nucleotide Polymorphism (SNP), either confirmed through SNP testing or by haplogroup prediction

using Short Tandem Repeat (STR) markers. However, that common ancestor is also shared by more than

60% of all Irishmen and that common ancestor lived more than 4000 years ago (Hay, 2017) – this

common ancestor is not relevant to our genealogical goal of identifying genetic descendants of Mahon

who lived around 1000 years ago. Likewise, several of the haplogroups found in the O’Mahony Surname

Project share a common ancestor in the haplogroup founder, but that founder will have lived much

more than 1000 years ago, too long ago to matter in this investigation.

Considering that the O’Mahonys descend from Mahon mac Cian who lived from about 980AD to

1038AD, we should look for haplogroups that would have been formed about 1000 years ago. Anything

older than that should be considered to be not genealogically related in the direct paternal line.

Using the SNP and STR based estimates for the Time to Most Recent Common Ancestor (TMRCA) within

each haplogroup, the participants in the O’Mahony Surname Project can be divided into groups that

may descend from an ancestor 1000 years before the present or earlier. These clusters can then be

examined for correlations with the O’Mahony historical record and with the geographic locations of

septs of the clan.

Geography Being the chiefs of the Eóganacht Raithlind, the O’Mahony lands in the 11th century were equivalent to

the Diocese of Cork:

“The Diocese of Cork, according to the Synod of Rathbreasil, which was held about 70 or 80

years after Mahon's death, extending ‘from Cork to Carn Ui Neid, and from the Abhain Mor

(Blackwater) to the southern sea.’” (O’Mahony, 1913)


The next several centuries, however, would see the O’Mahony lands shrink under the pressure from the

Norman invaders and the MacCarthys. The following summary of the O’Mahony septs and their lands is

drawn entirely from Rev. John O’Mahony’s (1913) work.

In the middle of the 13th century, following the murder of Muirchertach, chief of the O’Mahonys, at the

hands of Donal Gott MacCarthy in 1232, the O’Mahonys divided their lands between Muirchertach’s

brothers. The elder brother, Diarmid Mor O’Mahony, became the chief of the western O’Mahonys based

on the Mizen Head while Concobar O’Mahony became the chief of the eastern O’Mahonys Carbery with

their seat at Castle Mahon near Bandon. The lands between these eastern and western halves was

claimed by Donal Gott MacCarthy who made his son Donal Maol MacCarthy first Prince of Carbery.

The following generations of O’Mahonys would form several septs based on subdivisions of the

O’Mahony lands. Clan Fineen na Ceitherne is the earliest sept of the western O’Mahonys, named for

Fineen, the eldest son of Muirchertach O’Mahony. He was given lands in west Muskerry and Moviddy

parish; one branch of his descendants in the same lands became the O’Mahony Ruadh named after

Fineen’s grandson Donogh Ruadh O’Mahony. Adjacent to their lands, in the parishes of Kilmurray and

Kilmichael were the Clan Conogher, descendants of Conogher, grandson of Maghnus O’Mahony of the

Carbery branch.

To the west of Clan Conogher in the parish of Kilmichael were the lfflonloe sept, descendants of Tadhg

an Oir O’Mahony, brother of Diarmuid Mor O’Mahony II of the western O’Mahonys. This branch was

also known as O’Mahony an Oir (Irish for “the golden”) and would have septs of its own: O’Mahony an

Crochair for the descendants of Concobar an Crochair O’Mahony and O’Mahony Buidhe after Diarmuid

Buidhe O’Mahony.

When Diarmuid Mor O’Mahony II died in 1327, his eldest son Fineen became 5th chief of the western

O’Mahonys. Fineen chose not to honor his father’s arrangement that his brothers Donal and Diarmuid

should inherit lands and castles on the Mizen peninsula. Donal and Diarmuid left their homeland and

joined the MacCarthys, from whom Donal obtained lands in Kilnaglory and Diarmuid obtained lands in

County Kerry. The descendants of Donal became the O’Mahony of Kilnaglory sept and Diarmuid’s

descendants became the large sept “O'Mahony of the Sliocht Dermod Og” associated with several

locations in county Kerry.

Regrettably, nearly all of the O’Mahony lands were confiscated by the English and redistributed to

adventurers or Irish lords loyal to England following the rebellion of 1641. The Down Survey of Ireland

was undertaken at the direction of Oliver Cromwell in the years 1656-1658 to map the lands owned by

Catholics to be forfeited (Trinity College Dublin, 2013). The survey includes many of the O’Mahony land

owners of the late 1650s and is a valuable resource for determining where various branches of the

O’Mahonys lived prior to the loss of so many of their lands.

By mapping these sept lands from the Down Survey alongside the locations of the most distant known

paternal ancestors of the O’Mahony Surname Project participants, correlations between genetic groups

and septs sharing a common ancestor may become apparent.

Methods The dataset comprised of the Short Tandem Repeat (STR) data, terminal Single Nucleotide

Polymorphism (SNP) designation and reported paternal ancestor name, date and location for 142


participants of the O’Mahony Surname Project was collected from the public website hosted by Family

Tree DNA on 19 January 2017. To that data, the 67-STR-marker data for a single Mahoney participant

from YSEQ was added (designated Y7783 in the dataset), bringing the total number of participants to

143. In the interest of pursuing an unprejudiced, data-driven examination of the population, the

grouping information provided by the O’Mahony Surname Project administrators was discarded. The

only adjustments made to the STR data was the separation of multicopy markers into discrete values;

for example, DYS385=11-15 was separated into DYS385a=11 and DYS385b=15.

Using the terminal SNP designations provided by Family Tree DNA, eight participants who belong to

haplogroups outside of R1b were discarded from the dataset. Of these eight participants1, six had the

O’Mahony surname, or a variation thereof, but only two of these came from the same haplogroup (I-

P37). These eight participants are not closely related to any other O’Mahony Surname Project members

and, aside from the two I-P37 participants, these participants aren’t closely related to each other either;

they are likely O’Mahony clansmen in some other way, or the descendants of Non-Paternity Events

(NPEs).

For each remaining participants (n=135) who included location information for their Most Distant

Known Ancestor (MDKA) in Ireland, the civil parish and county was determined and a latitude and

longitude was geocoded for the centroid of the civil parish using the data provided by the Townlands.ie

database (2017). The resulting dataset of STR values and geocoded ancestor locations is available in

Supplemental Data 1.

William Howard (2009) suggested that 37-marker STR data is sufficient to separate a surname study’s

participants into their constituent haplogroups using genetic distance clustering. A script was written in

the R programming language to produce a hierarchical cluster dendrogram based on the first 37 STR

markers in the O’Mahony data set (see Supplemental Data 2). Two participants (kits 281423 and 94421)

could not be included in the dendrogram due to having less than 37 tested STR markers. The resulting

dendrogram (see Supplemental Data 3) was then compared to the terminal SNP designations for

participants who had undergone some manner of SNP testing: haplogroup clusters were designated by

building upwards from participants with SNP results such that members of each subtree contained at

least one positive result for a SNP in the haplogroup and no

member had a positive result for an SNP outside of the

haplogroup. In some cases, explained in the findings below, a

haplogroup cluster would be merged with a neighbor tree when

the haplogroup of the members in the neighbor tree could be

inferred (described in the findings). This method revealed eight

clusters of participants who had both similar STR results and for

whom there was sufficient SNP data to determine that they likely

belong to a distinct haplogroup downstream of L21 (Table 1).

Curiously, there are two separate clusters that both share the

CTS4466 haplogroup. These are labeled CTS4466a and CTS4466b

1 Kits excluded followed by FTDNA’s predicted haplogroup: 54645 – Baraban (Q-M242), 262295 – Cassidy

(R-M512), 293676 – Mahoney (E-CTS5637), 297541 – O’Mahony (I-M253), N94374 – O’Mahony (I-P37), 108376 – Mahoney (E-L117), 206249 – O’Manony (I-P37), 126867 – Mahoney (I-M223)

Haplogroup Participants

CTS4466a 23

CTS4466b 20

FGC5494 26

L226 13

P314.2 5

Z251 4

Z255 3

M222 3

Table 1: Number of participants in identified haplogroup clusters


in the diagram. Some potential reasons for this split are given in the findings below.

Conversely, there appears to be other clusters in the dendrogram, but they are among members who

haven’t done any SNP testing. Without SNP data, it’s not possible to know where these clusters begin

and end – whether the cluster represents participants who descend from a common ancestor, or

instead just represent similar STR results due to genetic drift.

For each of the eight identified haplogroup clusters, a map was created using the geocoded location

data. Where several participants descend from an ancestor in the same civil parish, the marker locations

were moved slightly to illustrate the cluster on the map.

Townlands owned by O’Mahonys in the Down Survey were added to the maps using the online data

from Trinity College Dublin (2013) using their “1641 Landowner Search” tool. It should be noted that

there were significant errors in the locations mapped by that tool when compared to the Terrier pages

for parishes where O’Mahony landowners were given. Townlands were mapped using the Townlands.ie

(2017) shapefile data. Additionally, the modern boundaries of the Diocese of Cork and Ross were added

to the map using the shapefile provided by the Central Statistics Office Ireland (2014) as an

approximation of the ancient boundaries of the O’Mahony lands at their greatest extent. The resulting

map of townland locations, with corrections by this author, are available as a .kmz file in Supplemental

Data 4.

There are two methods for using genetic data to find the Time to Most Recent Common Ancestor

(TMRCA): SNP counting and STR-based genetic distance calculations. The SNP counting method requires

results from Next Generation Sequencing (NGS) DNA tests such as Family Tree DNA’s Big Y and Full

Genomes Corporation’s Y Elite. The age of an SNP is estimated by counting the number of SNPs found

downstream of an SNP shared by several members, and multiplying by the average number of years

between mutations. Few O’Mahonys have undergone such a test, but we can use the SNP age estimates

from NGS results analyzed by YFull (2017) for some of the O’Mahony haplogroup clusters.

The STR method of calculating TMRCA uses the absolute difference in the observed counts of Short

Tandem Repeats (STR) over a number of locations on the Y chromosome (commonly 37, 67 or 111

marker locations), and calculates the average number of generations that would account for that

difference given the number of compared markers. This number of generations is then multiplied by the

average number of years between generations. This method is somewhat more speculative than the

SNP counting method due to the effects of genetic drift and the markers that are chosen for

comparison.

The STR data for each haplogroup cluster was loaded into Dean McGee’s Y Utility (2008) using the

infinite allele mutation model and McDonald mutation rates to create a matrix showing the estimated

TMRCA for each participant pair in the cluster. Estimates of TMRCA for specific identified SNPs in each

cluster were also retrieved from Yfull (2017) who use Next Generation Sequencing data for their

determination. For the large CTS4466 and FGC5494 clusters, a hierarchical cluster dendrogram was

created using the 67-marker STR data just for those members of the cluster who had tested that many

markers. This collection of information was examined alongside the historical record in an attempt to

find correlations between the septs of the O’Mahonys and the genetic data.


Findings Each of the eight haplogroup clusters is discussed separately below. The clusters CTS4466a and

CTS4466b are combined under their shared haplogroup: CTS4466. Each haplogroup heading is followed

by the list of SNPs downstream from L21 to the haplogroup of interest as listed on Alex Williamson’s Big

Tree (2017). If there is a popular name for the haplogroup, it is given in parenthesis after the SNP path.

The CTS4466 Branch L21/S145 > DF13 > FGC11134 > A353 > Z16250 > CTS4466/S1136 (Irish Type II)

Table 2: O'Mahony members of the CTS4466a and CTS4466b clusters

Kit Number

Name Paternal Ancestor Name County Parish Haplogroup Cluster

105419 Mahoney John Mahony; born early 1760s Cork Kilcummer R-M269 CTS4466a

108699 Ó Mathúna Jeremiah O Mahony c.1790 Cork Mourneabbey R-CTS4466 CTS4466a

134048 Mahoney Michael Mahony; b. 1820 d. 1910 R-M269 CTS4466a

134049 Mahoney Michael Mahony; 1840 R-M269 CTS4466a

134052 Mahoney Cork Kilmocomoge R-CTS4466 CTS4466a

134129 Mahoney R-M269 CTS4466a

181470 O'Mahony Jeremiah Mahony; 1870 Kerry Dromod R-M269 CTS4466a

190925 Mahony Florence Mahony b.1833 d.1910 R-M269 CTS4466a

194511 Mahoney John Smith Mahoney b 1760 R-M269 CTS4466a

206071 Mahoney R-M269 CTS4466a

206252 Mahony R-M269 CTS4466a

261030 O'Mahony R-M269 CTS4466a

298068 Willard James M. Willard Mahoney 1853-1936 R-A1338 CTS4466a

303560 Mahoney Cornelius Mahoney; b1808, d. 1880 R-A923 CTS4466a

378327 O'Mahony R-M269 CTS4466a

67716 Mahoney Patrick Mahoney; c.1824 R-A726 CTS4466a

83936 Mahoney Jeremiah Mahony; c.1820 Cork Carrigrohane R-M269 CTS4466a

87958 Mahoney Matthew Mahoney; b. 1810, d. 1895 Cork R-M269 CTS4466a

89269 Mahoney R-L21 CTS4466a

B6113 Mahoney R-M269 CTS4466a

N70882 Mahoney Patrick Mahony c.1850 Kerry Castleisland R-M269 CTS4466a

108700 Mahoney James Mahony early 1800's Kerry Castleisland R-M269 CTS4466b

115485 O Mahony Timothy Mahoney; 1773 Kerry Killarney R-FGC11150 CTS4466b

125840 O'Mahoney James Mahoney b.1800's Cork Inchigeelagh R-L21 CTS4466b

155017 O'Mahony O'Mahony; Cork c. 1800 Cork R-M269 CTS4466b

165440 Mahoney Cornelius Mahony; est. 1830 Cork Ballyclogh R-S1121 CTS4466b

181835 Mahoney Jeremiah Mahony; 1870 Kerry Castleisland R-M269 CTS4466b

184162 O'Mahony Cork Cork R-M269 CTS4466b

184166 Mahoney Cork Fanlobbus R-M269 CTS4466b

193092 Mahoney Cork Kilmocomoge R-L21 CTS4466b

204577 O Mahony Timothy Mahony; born c. 1798 Kerry Killarney R-CTS4466 CTS4466b

204578 O Mahony Timothy Mahony; born c. 1798 Kerry Killarney R-CTS4466 CTS4466b

208127 Mahoney James Mahoney 1853 Kerry Killarney R-L21 CTS4466b

250250 Mahoney Denis Mahoney; b. 1820, d. 1901 R-S1121 CTS4466b

336553 O'Mahony James J. O'Mahony VI; b. 1954, d. 2001

Cork Kilmocomoge R-A150 CTS4466b

351085 Mahoney Timothy Mahoney; b. 1860 R-M269 CTS4466b

88090 Mahony Timothy Mahony born c. 1860 Cork Ballymodan R-CTS4466 CTS4466b


This haplogroup is common in southern Ireland and researchers have labeled it “Irish Type II”. It was first

identified as an STR cluster, with the defining CTS4466 SNP discovered in 2012 (R1b-CTS4466 Plus

Project, 2017). Like the O’Mahonys, many of the other families in this haplogroup have surnames

associated with the Eóganachta clans: MacCarthy, O’Sullivan, Donoghue and Driscoll. All members of the

CTS4466 subclade are predicted to have a common ancestor who lived about 2200 years ago (YFull,

2017) – too long ago to share a genealogical connection, but in a time frame that supports the notion

that this haplogroup would be part of the Eóganachta tribe.

CTS4466 is the largest haplogroup represented in the O’Mahony Project when combining the CTS4466a

and CTS4466b clusters (n=43), though not all claim decent from a Mahony: removing the Cremeans,

O’Reilly, Coakley and Wise kits results in the 37 kits given in Table 2.

The split of the CTS4466 haplogroup among the a and b clusters may be due to members of haplogroups

who, through genetic drift, have STR marker values similar to those found in the CTS4466 haplogroup.

The split may also be due to the use of only 37 markers to create the initial dendrogram, perhaps

selecting markers with a higher variability in this haplogroup. To examine the later possibility, a

dendrogram was created using the 67-marker STR data for the 29 participants for whom that data was

available. The resulting clusters are the same, with each member belonging to the same a or b group as

in the 37-marker dendrogram (Figure 1).

Figure 1: 67-marker dendrogram of CTS4466 O'Mahony DNA Project members.

Fortunately, several of the members of the CTS4466 group have undergone advanced SNP testing, and

this helps to subdivide the group into distinct branches – members considered to share a genealogical

connection should be on a branch of the haplotree that formed no more than 1000 years ago. For the


sake of subdividing the CTS4466 O’Mahonys, those who share a genealogical connection must, at a

minimum, all belong to the same subclade as represented by the SNPs on the rightmost column of the

simplified CTS4466 haplogroup chart (Figure 2).

Figure 2: Simplified CTS4466 haplogroup chart. Branches are identified by SNP names and the date of the branch formation is given in Years Before Present (ybp) for branches noted on YFull's YTree v5.03.

The distinct split between the CTS4466a and CTS4466b clusters can be better explained when compared

with the haplotree. All members of the CTS4466b cluster who have undergone advanced SNP testing are

positive for one of the SNPs along the branch S1121>A150>FGC11150. This suggests that the members

of the CTS4466b cluster may be the descendant of a single ancestor who may have existed in a

genealogical timeframe.

The CTS4466a cluster has members from several different subclades of CTS4466 that split long before

the adoption of surnames. There are certainly subgroups within the CTS4466a cluster representing

members who share a recent common paternal ancestor (the kits 134129, 134052, 134048, 134049 and

89269 being a clear example who may also share a genealogical ancestor with kits 303560 and 105419),

but these subgroups will not have shared a genealogical ancestor with each other or with the members

of the CTS4466b cluster. In short, the CTS4466a cluster contains several unrelated family lines.

Of the O’Mahony CTS4466 kits, 22 of them provided a location for their most distant known ancestor.

The map of these locations reveals some patterns that may help identify the septs that these members

belong to (Figure 3). There are clusters of O’Mahonys in the Castleisland (n=3) and Killarney (n=4)

parishes and another O’Mahony in Dromod parish, all in county Kerry. Separately, there is a group of

three kits in north Cork well outside of traditional O’Mahony lands: one kit each in the parishes of

Ballyclogh, Kilcummer, and Mourneabbey. The history of the O’Mahonys may explain these two clusters.

CTS4466 (3700ybp)

A541 (2200ybp)

S1121 (1700ybp)

Z16521 (1700ybp)

A150

FGC11150

A745 A159

(1450ybp)

A195 A761

A88 (1700ybp)

Z16254

A212


Figure 3: Locations of the most distant known ancestor for CTS4466 O'Mahonys. The red shaded areas are townlands owned by O’Mahonys in the Down Survey and the black bordered region is the modern Diocese of Cork and Ross.

Diarmuid Mor O’Mahony, fourth chief of the western O’Mahonys, died in 1327AD. Before his death, he

promised Rosbrin Castle and its surrounding land to his two younger sons, Donal and Diarmuid Og.

However, when his eldest son Fineen became the chief upon his father’s death, he refused to hand over

the castle and lands to his brothers. The brothers left Ivagha, along with some of their clansmen, and

took up with MacCarthy Mor.

MacCarthy gave lands in Barrett’s Country (i.e. the Barony of Barretts) to Donal, and later more lands in

Kilnaglory just outside of Cork City. The descendants of Donal would become the septs O’Mahony of

Kilnaglory and, in Barrett’s Country, O’Mahony of Concobar Dubh. To the three kits in the Ballyclogh,

Kilcummer, and Mourneabbey parishes, we could perhaps add the kits in Carrigrohane parish and Cork

City, the latter two being near to Kilnaglory parish. If these five kits (165440, 105419, 108699, 83936 and

184162, collectively called the “north Cork group”) are closer genetically to each other than to the other

CTS4466 kits, then the evidence points to this group as being descendants of Donal, son of Diarmuid

Mor O’Mahony.

The Kerry branch is easier to define – all the Kerry O’Mahonys are said to be descendants of Donal’s

brother Diarmuid, known as Diarmuid Og of Desmond. This branch has been written about extensively,

and many members of this branch have become somewhat famous in Irish history. The Reverend John

O’Mahony (1913) writes:

“[Diarmuid]’s descendants gradually acquired a large extent of land, and had multiplied so

considerably that (as we shall see later on), in a State Paper of the Tudor times, they are

described as a "populous Sept." Sept organization, in the strict sense of the term, was of course


not possible for them in a Tribeland not their own, but at the period referred to, the Head of the

Family was looked up to by his multitudinous kinsmen, and through them wielded considerable

influence. The Branch survived the downfall of the parent Septs of Ivagha and Kinelmeky, and of

the Sept of MacCarthy More; it did not sink into obscurity even in the Penal Days, and

contributed a large number of highly distinguished officers to the Irish Brigade in the service of

France and Spain.”

As with Donal’s branch, if the Kerry O’Mahonys in the CTS4466 haplogroup are descended from

Diarmuid, we should expect them to have a closer genetic relationship to each other than to the other

CTS4466 O’Mahonys.

Returning to the genetic data, if the north Cork group and the Kerry group are to be considered

descendants of Donal and Diarmuid, then they must be members of the same genetic cluster –

CTS4466a or CTS4466b. This comparison (Table 3) does show that the majority of the Kerry group (6 out

of 8) are members of the CTS4466b cluster, as well as 2 of the 5 north Cork members. As shown above,

the members of the CTS4466b cluster may descend from a common genealogical ancestor. What’s

more, the six members of the Kerry group share a subtree in the CTS4466b cluster that is distinct from

the subtree shared by the two members of the north Cork group. The small sample size is a limitation

here, but it is intriguing to suppose that this cluster might correlate to the historical Donal and Diarmuid

Og O’Mahony.

Kit Civil Parish County Geographic group Cluster Haplogroup

165440 Ballyclough Cork North Cork CTS4466b R-S1121

105419 Kilcummer Cork North Cork CTS4466a R-M269

108699 Mourneabbey Cork North Cork CTS4466a R-CTS4466

83936 Carrigrohane Cork North Cork CTS4466a R-M269

184162 Cork City Cork North Cork CTS4466b R-M269

N70882 Castleisland Kerry Kerry CTS4466a R-M269

108700 Castleisland Kerry Kerry CTS4466b R-M269

181835 Castleisland Kerry Kerry CTS4466b R-M269

204578 Killarney Kerry Kerry CTS4466b R-CTS4466

115485 Killarney Kerry Kerry CTS4466b R-FGC11150

208127 Killarney Kerry Kerry CTS4466b R-L21

204577 Killarney Kerry Kerry CTS4466b R-CTS4466

181470 Dromod Kerry Kerry CTS4466a R-M269

Table 3: Kits in the north Cork and Kerry geographic groups along with their CTS4466 cluster and FTDNA Haplogroup.

The three remaining north Cork kits are all members of the CTS4466a cluster, but only two of them

share a subtree: kits 108699 and 83936. Similarly, the two Kerry group kits in the CTS4466a cluster share

a subtree, but most of the members of that subtree have not undergone SNP testing or STR testing for

more than 37 markers, so drawing any conclusions about this subtree is difficult.

Considering the possibility that the CTS4466b cluster represents the descendants of a common

genealogical ancestor, the 37-marker STR data for the members of this cluster was examined using Dean

McGee’s Y-Utility (2017). The resulting Time to Most Recent Common Ancestor (TMRCA) estimate for

each pair of kits is given in Figure 4 using the infinite allele model and Doug McDonald’s mutation rate

with a generation age of 30 years. The TMRCA estimates are quite rough given the small number of STR

locations and the number of estimated values used in the calculation, but this shows that the cluster, as

a whole, is possibly older than the time of surname adoption. However, the TMRCA estimates for


members of subgroups in the cluster are in the range that might be expected for the descendants of

Diarmuid Og and Donal. For example, the maximum TMRCA for members of the Kerry subgroup is 810

years before present, or about 1207AD and the father of Donal and Diarmuid, Diarmuid Mor O’Mahony,

died in 1327AD.

Figure 4: CTS4466b cluster Time to Most Recent Common Ancestor estimates using Dean McGee's Y-Utility.

Altogether, the analysis of the CTS4466 O’Mahonys shows that, within the O’Mahony Surname Project,

the haplogroup represents several families who are not genealogically related on the paternal line. One

particular cluster of O’Mahonys, CTS4466b, may share a common genealogical ancestor, and the

locations of the member’s known ancestors suggest a descent from Diarmuid in Kerry, and possibly

Donal in Cork. Members of the CTS4466b cluster who haven’t undergone advanced SNP testing should

be encouraged to do so by ordering the R1b-CTS4466 SNP Pack from Family Tree DNA. Single SNP tests

for A150 and FGC11150 are a less expensive option from YSEQ.net for members of this cluster as well.


There is not enough SNP testing among the O’Mahonys in the CTS4466a cluster to determine how many

distinct family groups there might be within the cluster, though it is clear that there are some close

relatives within this cluster. All members of this cluster would benefit from the CTS4466 SNP Pack. Next

Generation Sequencing (NGS) tests like Big Y would also be helpful for members of this cluster, but this

should be pursued with input from project administrators, especially when testing members with a

known genealogical relationship.

The FGC5494 Branch L21/S145 > DF13 > FGC5494

The FGC5494 SNP was discovered in January 2014 (Jost, 2014) – quite recently compared to the defining

SNPs for the other O’Mahony haplogroups. With 26 participants, this is the second largest genetic

cluster in the O’Mahony DNA Project after CTS4466. Unlike CTS4466, M222 and others, this haplogroup

has a broad distribution throughout the Isles as well as on the European continent (Williamson, 2017),

making it more challenging to associate it with any particular historic group of people.

Table 4 O'Mahony members of the FGC5494 haplogroup cluster.

Due to its recent discovery, FGC5494 was not included in early SNP tests offered by Family Tree DNA,

leaving participants who pursued SNP testing with a terminal SNP designation of its parent haplogroup:

Kit ID Name Paternal Ancestor Name County Civil Parish Haplogroup

358827 Mahoney Jeremiah Mahoney b. abt 1825 Cork Abbeystrowry R-M269

181462 O'Mahony O'Mahony; 1885 Cork Ballymodan R-M269

181469 O'Mahony O'Mahony;1800s Cork Carrigaline R-M269

177431 O'Mahony O'Mahony Cork Cork R-L21

453266 Mahony Denis Mahony b. 1788 Cork Dromoaleague R-M269

181471 O'Mahony George O'Mahony; 1790 Cork Dromoaleague R-DF13

96190 Mahoney John O'Mahony; 1821 Cork Fanlobbus R-M269

84564 Mahaney Thomas Mahony b.1813 Cork Fanlobbus R-M269

108701 Mahoney Cain Patrick Mahony; c. 1835 Kerry Killarney R-L21

96288 Mahoney Cornelius Mahon[e]y 1790-1872 Cork Kilmoe R-M269

68777 Mahoney Cornelius Mahony; b. 1828 Cork Kilmoe R-L21

228205 Mahany Cain Mahony; b.1814 Cork Kilmurry R-L21

183194 Mahoney Timothy Mahony; b. abt 1765 Cork Midleton R-FGC5494

89776 O'Mahony Denis O'Mahony c. 1820 Cork Rathbarry R-L21

204574 O'Mahony O'Mahony; pre 1880 Cork Ross R-M269

226327 O'Mahony R-M269

126083 Mahoney Edward Joseph Mahoney; b 1878 R-M269

108698 Mathúna O'Mahony R-M269

188328 Mahoney R-M269

188325 Mahoney Daniel William Mahoney;1841 R-DF13

153041 Mahoney Mahony R-M269

117777 Mahoney Denis Mahony R-L21

188321 O'Mahony R-M269

222841 LeCuyer Jean Baptiste LeCuyer b.1813 R-L21

123804 Mahany John Mahony; c.1815 Cork R-M269

Y7783 Mahoney Jeremiah Mahony; b. about 1790 Cork Inchigeelagh R-FGC5494


DF13. This isn’t to say that all participants previously designated as DF13 would be positive for FGC5494,

but having STR results close to confirmed FGC5494+ kits and a tested terminal SNP of DF13 is an

indicator that a participant is likely to belong to the FGC5494 haplogroup. This is likely the case for kits

188325 and 181471.

The first O’Mahony participant to pursue testing for the FGC5494 haplogroup was kit Y7783 in 2016

through YSEQ’s FGC5494 SNP Panel. The results returned a positive call for the FGC5494 SNP, but

negative calls for all downstream branches, indicating that the FGC5494 O’Mahonys represent a newly

discovered branch downstream of FGC5494. A second O’Mahony participant, 183194, followed up with

a single SNP test for FGC5494 through Family Tree DNA and also received a positive result.

To investigate the possibility of FGC5494 O’Mahonys belonging to several distinct subclades of the

haplogroup as in the CTS4466 cluster, a dendrogram was created using the 37-marker STR data for the

26 O’Mahonys in this cluster along with the 37-marker STR data for 154 participants of the FGC5494

Haplogroup Project at Family Tree DNA who had confirmed positive results for FGC5494 and

downstream markers (Supp. Data 5). The dendrogram shows O’Mahonys as a distinct cluster within the

haplogroup, suggesting that all 26 O’Mahony participants in this cluster share a genealogical ancestor.

Location information is available for 17 of the 26 kits in the O’Mahony FGC5494 cluster. Mapping these

locations does not result in any geographic clusters, but the participants are spread throughout the

lands in Cork where the O’Mahonys traditionally lived: from Cork to the Mizen Head (Figure 5). Of

particular note are two participants whose most distant known ancestor lived on the Mizen peninsula in

Kilmoe parish, land associated with the chiefs of the western O’Mahonys. The participant in Kilmurry

Figure 5: Locations of the most distant known ancestor for FGC5494 O'Mahonys. The red shaded areas are townlands owned by O’Mahonys in the Down Survey and the black bordered region is the modern Diocese of Cork and Ross.


parish, kit 228205, has recorded an association with the O’Mathuna Ceitherne sept which held land in

Kilmurry and was also an early sept of the western O’Mahonys. The only FGC5494 O’Mahony outside of

County Cork is kit 108701 in Killarney.

When analyzed using Dean McGee’s Y-Utility (2017), the estimates for the Time to Most Recent

Common Ancestor (TMRCA) for all 26 of the FGC5494 O’Mahony participants reaches a maximum of

1440 years before present, or about 577AD (Figure 6). This estimate is higher than expected for there to

be a genealogical relationship, but all participants in this cluster have more recent TMRCA estimates

with subsets of this cluster. It could be the case that not all participants in this cluster are truly members

of the FGC5494 haplogroup as assumed, though that is somewhat contradicted by the O’Mahony cluster

including all of these kits when compared to the FGC5494 Haplogroup Project participants. It is clear

that more SNP testing is necessary to permit further investigation of this cluster.

If the O’Mahonys in this cluster can be shown to share a single subclade of the FGC5494 haplogroup

through further SNP testing, then this cluster would be the largest single family group within the

O’Mahony DNA Project. The association between some of the kits in this cluster and the western

O’Mahonys coupled with the old TMRCA estimates suggest that this cluster could represent the

descendants of Diarmuid Mor I if not his forebears.

Figure 6: FGC5494 cluster Time to Most Recent Common Ancestor estimates using Dean McGee's Y-Utility.


To continue research on this cluster, it is necessary for at least two participants undergo a Next

Generation Sequencing test such as the Big Y from Family Tree DNA or Y Elite from Full Genomes Corp.

The results of these tests will reveal the novel SNPs that represent the O’Mahony subclade of the

FGC5494 haplogroup. Individual SNP tests could then be developed for these unique markers to allow

other participants to confirm their suspected membership in this cluster. Until these new markers are

discovered, members of this cluster should not order the FGC5494 SNP Pack from Family Tree DNA or

the FGC5494 SNP Panel from YSEQ, but should be encouraged instead to order a single SNP test for

FGC5494 if they do not plan to order a NGS test.

The M222 Branch L21/S145 > DF13 > Z39589 > DF49/S474 > Z2980 > Z2976 > DF23 > Z2961 > M222

The M222 SNP is the defining marker for one of the largest haplogroups in Ireland. Originally, all men

positive for M222 were thought to be descendants of Niall of the Nine Hostages, King of Tara and

ancestor of the O’Neill dynasty in northern Ireland (R-M222 and Subclades). Further research has shown

this to be unlikely, but the haplogroup does have a high frequency in northern Ireland and Scotland.

M222 is a subclade of DF49 and has a TMRCA of 100AD (YFull, 2017). Three kits in the O’Mahony DNA

Project are predicted to be positive for M222 (Table 5).


181464 O'Mahony Cork Kilmocomoge (R-M269)

84511 Maney Jeremiah Mahony; b. about 1772 Cork Kilmoe R-FGC8739

74127 Mahoney Daniel Mahoney; b.1811 (R-M173) Table 5: O'Mahony participants in the M222 haplogroup cluster.

Through correspondence with the owner of

kit 84511, a family tradition revealed that his

paternal ancestors were known as

“O’Mahony Finn” (Maney, 2016). Kits 84511

and 181464 have a genetic distance of 1

from each other at 37 markers (DYS460 11 vs

12), indicating that they share an ancestor

born about 240 years ago. An intersection

between the family trees of these two men

has not been found, but they both descend

from men who lived on land associated with

the O’Mahony Fionn sept (Figure 8).

Kit 74127 has a genetic distance, at 37

markers, of 7 from the Maney kit and 8 from

the O’Mahony kit, giving a predicted time to

most recent common ancestor of 1110 and

1290 years respectively (Figure 7). Without

SNP testing, it is difficult to say whether this

kit may be genealogically related to the

other participants in the M222 cluster.

Figure 7: Estimated time to most recent common ancestor for the M222 kits in the O’Mahony DNA Project.


The owners of kits 181464 and 84511 likely both descend from a common O’Mahony ancestor who was

a descendant or relative of Conor Fionn O’Mahony (d. 1513). This ancestor likely lived in the late 17th

century.

This cluster stands apart in the O’Mahony Surname Project for having a robust family history that

connects it to lands held by an identified sept with whom a most-distant-known-ancestor is also

identified. The O’Mahony Fionn sept saw the last of the chiefs of the western O’Mahonys, direct

descendants of Mahon. However, the two members of the cluster who are likely genealogically related

share an ancestor who probably lived right at the time that the chiefs of the western O’Mahonys saw

their lands confiscated.

There is a Mahan kit (FTDNA: 279864) who is M222>DF85+ which is just upstream from the terminal

SNP of kit 181464 (Williamson, 2017). The owner of the Mahan kit has not joined the O’Mahony DNA

Project, but they may prove to be a relative of this branch. If kits 74127 and 181464 get positive calls for

the DF85 or downstream SNPs, then this cluster could confidently be expanded and the TMRCA

reexamined to get a better sense of how the M222 haplogroup relates to the O’Mahony Fionn sept and

the larger O’Mahony history.

Figure 8: Locations of O’Mahonys in the M222 (purple), P314.2 (yellow), Z251 (green) and Z255 (teal) haplogroup clusters. Kit 377582 in Galway, a member of the Z255 cluster, is not shown. The red shaded areas are townlands owned by O’Mahonys in the Down Survey and the black bordered region is the modern Diocese of Cork and Ross.


The L226 Branch L21/S145 > DF13 > ZZ10 > Z253 > Z2534 > ~22280136-C-G > L226 (Irish Type III)

This branch of the O’Mahonys has been well explored by Gwynneth Bennet (2015) and Brian Sayers

(2005). The majority of kits in this haplogroup descend from an ancestor in the Mitchelstown and

Kilbeheny areas (Figure 11) near the junction of counties Cork, Limerick and Tipperary.


172904 Mahony John Mahony; c.1836 Kerry Aglish R-L226

211765 O'Mahony O'Mahony Cork Brigown R-L226

181468 O'Mahony Thomas Mahony; 1825 Cork Brigown R-M269

45180 O'Mahony Daniel Mahony b.c. 1835 Tipperary Carrick R-M269

12109 Lloyd Michael Mahoney; b. ca. 1800 Limerick Kilbeheny R-M269

184164 O'Mahony Thomas O'Mahony Limerick Kilbeheny R-M269

184165 O'Mahony William O Mahony Cork Wallstown R-L226

97012 Mahoney Daniel Mahoney R-Z253

204576 O'Mahony Jeremiah Mahony b. 1844 R-M269

156885 O'Mahony R-DC198

191654 Mahony John O'Mahony b. 1807 R-L226

233639 Mahoney R-M269

232192 O'Mahony R-L226 Table 6: O'Mahony participants in the L226 haplogroup cluster.

A cluster analysis of the STR data at 37 markers

reveals that there is a distinct group of L226 kits

who share a recent common ancestor: 156885,

12109, 184165, 191654, 232192, 45180, 184164,

181468 and 211765. The remaining kits – 172904,

97012, 233639 and 204576 – have a larger genetic

distance from each other (Figure 9).

Kits 172904 and 97012 have a genetic distance of 3

from each other, but a genetic distance of 8 to 12

from the other kits in this cluster. Kit 172904

descends from an ancestor near Killarney in County

Kerry, but the ancestor location for kit 97012 is

unrecorded. These two kits likely share a common

ancestor in the last 500 years, but are unlikely to

be genealogically related to the rest of the L226

group. Both of these kits would benefit from

additional SNP tests to determine if they share a

more recent SNP downstream of L226.

Figure 9: Genetic Distance matrix for L226 kits using 37-marker STR data.


Kits 233639 and 204576 do not have any

match in this group with a genetic distance

less than 6, including to each other. The most

distant known ancestor’s location is not

recorded for either of these kits. It’s possible

that these kits are distantly genealogically

related to others in the L226 group, but

there’s not enough data to determine this. Kit

233639 only has 37 STR markers tested, but

kit 204576 has 67 STR markers available.

A second analysis was run using the 67-

marker STR data. Kits 172904 and 97012 were

excluded from this run due to their large

genetic distance and unlikely genealogical

relationship from the rest of the group. Kits

233639 and 181468 were excluded because

they only have data for 37 markers. The

predicted time to most recent common

ancestor for the remaining kits is shown in

Figure 10.

The 67-marker analysis doesn’t help bring kit 204576 any closer to the others in this group. It’s possible

that this kit descends from a very early shared ancestor, but it could also be a coincidental connection.

Further SNP testing is advised for this kit.

The other kits in this group clearly descend from a common ancestor who lived about 480 years ago. In

Bryan Sayers (2005) article, he identifies an early patriarch in Kilbeheny as Tomás O’Mahony of Ardglas

who likely lived in the early 1700s – his son Thomas Og O’Mahony already had three sons when he

leased land in Clonkilla in 1782. It may be the case that Tomás, or perhaps his father or grandfather, is

the direct common ancestor for this branch of the family.

Sayers offers that this branch of the O’Mahonys may descend from Fineen, brother of Diarmuid

Spaineach, chief of Carbery. Fineen is said to have been established in the Fitzgerald lands of North

Munster. Sayers also cites the conjecture of historian Mainchín Seoighe that, “the first Kilbeheny

O’Mahony and/or his descendants served the White Knights in some significant capacity.”

In terms of genetics, the Kilbeheny O’Mahonys benefit from the Big Y test of kit 156885. Through this

kit’s results, it is clear that the Mahony participants in this cluster – 156885, 12109, 184165, 191654,

232192, 45180, 184164, 181468 and 211765 – should all be positive for the DC28 SNP. Should another

participant in this group get a Big Y test, it will allow the group to establish new SNPs downstream of

DC28 which can then be individually tested by the rest of the group members to build a genetic tree to

compare with the family history of this group. As of Jan 26, 2017, a McDonough kit has also tested

positive for DC28 as well as a new downstream SNP: DC199 (17141477-A-G) (Williamson, 2017). This

may help the O’Mahonys in this branch identify a point of origin for this family.

Figure 10: Time to Most Recent Common Ancestor for L226 kits with 67-marker STR data.


Figure 11: L226 O’Mahonys who provided a location for their most distant known ancestor, mapped to the Civil Parish.

The L226 SNP is the defining SNP for the genetic group labeled “Irish Type III” by researchers in the

genetic genealogy community. This haplogroup is a subclade of Z253, and has been associated with the

Dál gCais (O’Brien Surname Project). In particular, the DC33 subclade of L226 is dominated by O’Briens

and is a candidate for the haplogroup to which Brian Boru belonged. Brian was preceded in kingship by

his elder brother Mahon (Irish: Mathgamain mac Cennétig), and the MacMahon’s are said to descend

from him (O’Hart, 1892). Indeed, we find a McMahon on another subclade of L226: kit 2930082. Perhaps

this branch of O’Mahonys are descendants of Mahon, King of Munster rather than a branch of the

Eóganachta O’Mahonys. The annals mention that Mahon died in 976 AD, so if this branch of the

O’Mahonys descend from him, it might explain the larger genetic distance between some of the kits in

this cluster. It is too early in the field of genetic genealogy to match a specific SNP to a historical figure

like Mahon or Brian – if indeed it will ever be possible – but the L226 branch of the O’Mahonys would

benefit from advanced SNP testing to help discover new SNPs and establish which of those new SNPs

are unique to the O’Mahony branch.

2 http://www.ytree.net/SNPinfoForPerson.php?personID=296


The P314.2 Branch L21/S145 > DF13 > DF21/S192 > FGC3213 > Z16532 > Z16526

The P314.2 branch forms a distinct cluster within the O’Mahony Surname Project Data, but the kits in

this group don’t have a close genetic distance to each other, at least at the 37-marker level that most of

them have tested. If these kits share a common genealogical ancestor, then that ancestor must have

lived quite some time ago.


84534 Mahoney James Mahony; born c. 1800 Cork Fanlobbus R-P314

164296 O'Mahony Mahony R-M269

314915 Mahoney Jeremiah Mahoney; born c. 1802 Cork Desertserges R-M269

399520 Mahoney Dennis Mahoney Cork R-M269

13771 Mahoney John Mahoney b. abt 1830 Cork R-ZS4598 Table 7: O'Mahony participants in the P314.2 haplogroup cluster.

Only two of these kits provided a detailed location for their most distant known ancestor, but those

locations are both in the regions of Cork where we would expect to find O’Mahonys of the

Carbery/Kinelmeky branch (Table 7).

Fortunately, kit 13771 has taken a Big Y test

which reveals quite a bit more information.

The Big Y results place this kit in the ZS4598

branch downstream of P314.2. This branch is

convincingly associated with the

MacCarthys, and the ZS4598 SNP in

particular is believed to have originated with

Donall Gott Mac Cárthaigh, progenitor of the

MacCarthy Reagh dynasty, who died in 1251

(McCarthy, 2016). By virtue of the positive

result for ZS4598 in kit 13771, the

MacCarthy DNA Project has incorporated the

results of all the P314.2 O’Mahony kits into

their analysis. Kits 399520 and 84534 are

designated as likely positive for ZS4598. Kits

314915 and 13771 are likely positive for the

ZZ50 SNP downstream of ZS4598 and likely

share additional downstream SNPs. Kit

164296 needs more STR data to be placed

with confidence on the MacCarthy tree.

This group provides an interesting

opportunity to compare the estimated time to most recent common ancestor based on STR results. If

the MacCarthy Project admins are correct that ZS4598 originated with Donall Gott MacCarthy, then the

most recent common ancestor lived no more than 850 years ago. However, the 37-marker STR

Figure 12: Time to Most Recent Common Ancestor for P314.2 kits with 37-marker STR data.


estimates place the most recent common ancestor of the P314.2 O’Mahonys at up to 1800 years ago

(Figure 12). This is not a refutation of the conclusions of the MacCarthy DNA Project, but it does indicate

the necessity in using both STR and SNP data along with established family history when trying to

establish a possible genealogical connection between kits.

The history of the O’Mahonys is riddled with connections, and sometimes confrontations, with the

MacCarthys (O’Mahony, 1913). Donal Mór MacCarthy, father of Donall Gott, was a contemporary of

Donogh na Himerce O’Mahony, the progenitor of all the septs of the O’Mahonys. These two were heads

of rival factions in bitter fighting all across southern Ireland in the early 1200s. In 1232, this culminated

in the murder of Muirchertach O’Mahony, eldest son of Donogh na Himerce, at the hands of Donall Gott

MacCarthy. Muirchertach was the first O’Mahony to be known as “of Carbery”, a title which was then

placed upon Donall Gott, first to be called “Prince of Carbery”. Muirchertach’s brother, Concobar

O’Mahony, became the chief of the Kinelmeky O’Mahonys, who were from then on known as the

O’Mahonys of Carbery.

The MacCarthys were a powerful presence in south west Cork from the 13th century onward. Though

there were other conflicts between the MacCarthys and the O’Mahonys, there was also peace. In the

16th century, Honor O’Mahony, daughter of Conor Finn O’Mahony of the western sept married Cormac

MacCarthy, and Fineen O’Mahony, chief of the Kinelmeky sept, married a sister of MacCarthy Reagh.

Conogher, the son of this later marriage would, however, be involved in long dispute with the

MacCarthy Reaghs over ownership of land in Kinelmeky. As discussed in the CTS4466 haplogroup section

above, it was through MacCarthy Mor that Donal and Diarmuid were given lands in north Cork and

Kerry.

This history doesn’t suggest a particular ancestor, time, or location for the ancestors of the P314.2 kits,

but it does show that there was a long and complicated history between the O’Mahonys and the

MacCarthy Reaghs. The P314.2 O’Mahonys are likely the result of one or more non-paternal events

between these two families. The results of the MacCarthy DNA Project support the notion that at least 4

of the 5 kits in this cluster share the ZS4598 SNP that designates direct genetic descent from Donall Gott

MacCarthy. The ancestral location of the 314915 kit suggests a connection to the O’Mahony of Carbery

sept, but the Dunmanway location for the ancestor of kit 84534 is more difficult to associate with any

particular O’Mahony sept.

Kits 84534, 164296, 314915 and 399520 would benefit from SNP testing for ZS4598 as well as SNPs

upstream and downstream of this location on the haplotree (such as the R1b-DF21 SNP Pack offered by

Family Tree DNA). The results of this testing will significantly help place these kits in relationship to each

other and point the way to one or more common ancestors in the rich historical record between the

O’Mahony and MacCarthy Reagh families.

The Z251 Branch L21/S145 > DF13 > Z39589 > Z251/S470 > S11556 > S9294 > BY3231 > Z18092

The Z251 haplogroup is similar to the FGC5494 haplogroup in that they both have a broad geographic

distribution both in the Isles and on the European continent. Likewise, this haplogroup was also

discovered more recently, Family Tree DNA only making SNP testing available for it since late 2015 (R-

Z251 and Subclades). The O’Mahonys in this cluster are based around kit B41011 who has tested

positive for the Z18092 subclade of Z251. The other three kits in this cluster haven’t done extensive SNP


testing, but are likely also members of the Z18092 subclade as well considering the close genetic

distances in this cluster (maximum GD of 3 at 37 markers).


B41011 Mahoney Timithy Mahony b. abt 1824 Cork Kilgarriff R-Z18092

203836 Matheny John Mahany b. abt 1810 R-M269

162588 Mahoney O'Mahoney Cork Ballymodan R-L21

226329 O'Mahony Michael O Mahony R-M269 Table 8: O'Mahony participants in the Z251 haplogroup cluster.

Only two of the kits in this cluster have a location for their most distant known ancestor, but they are

both in the eastern portion of the O’Mahony territory, suggesting a relationship with the O’Mahony

Carbery branch. The time to most recent common ancestor estimates give a maximum of 510 years

before present; this places the formation of this branch of O’Mahonys at the time of Fineen O’Mahony

Carbery, chief of the eastern O’Mahonys until his death in 1579. This was a tumultuous time for the

eastern O’Mahonys as they rebelled against the English “undertakers” who were claiming land in County

Cork. The O’Mahonys were among many noble Irish families fighting to retain their lands and it was in

this fight that Conogher, son of Fineen, was slain in 1582, having been chief of the eastern O’Mahonys

for just three years (O’Mahony, 1913). Upon Conogher’s death, his cousin Donal Graney O’Mahony

became chief of the eastern O’Mahonys.

Rev. John O’Mahony (1913) expresses some

uncertainty about Donal Graney’s parentage.

He is said to be the son of Cian who was

brother to Fineen who died in 1579, but it’s

unclear who his mother was. In any case, he

appears to be a cousin of Conogher’s who had

been leading the O’Mahonys in the rebellion.

Donal continued the O’Mahonys fight against

the English, burning down the family’s own

Castle Mahon near Bandon rather than

allowing it to fall into the hands of the English

adventurer Phane Beecher. Like Conogher

before him, Donal Graney was slain in the

rebellion.

Richard Harrison, lawyer for Phane Beecher,

wrote in a letter, “The whole nation of

O'Mahons is to be suspected, for they do

pretend title (i.e., maintain) and are brothers

and cousins of the traitor, Daniel Graney

O'Mahon” (cited in O’Mahony, 1913).

Harrison’s account is certainly biased by his duty to advocate for Beecher’s ownership of the lands, but

this account does reveal that there was a period in the late 1500s where ownership of the eastern

O’Mahony lands was in question, and there may have been an opportunity for relatives of Donal Graney

Figure 13: Time to Most Recent Common Ancestor for Z251 kits with 37-marker STR data.


to claim a closer relationship than existed. Perhaps also there were men who fought with Conogher and

Donal Graney in the rebellion who were then invited to join the O’Mahony clan in some manner.

There is not enough data on the Z251 O’Mahony cluster to draw any firm conclusions on the origin of

this branch, but the data provided does suggest that this branch may have joined the O’Mahony Carbery

branch around the time of the Desmond rebellions. Participants in this cluster should consider testing 67

or 111 STR markers to provide a more accurate estimate for the time to most recent common ancestor

for this branch. This cluster, in particular, would benefit greatly by providing more genealogical

information to try to identify common ancestors or locations.

The Z255 Branch L21/S145 > DF13 > ZZ10 > Z255 (Irish Sea)


377582 Mahon Patrick Mahon; b. abt 1775, d. abt 1850

Galway Dunmore R-M269

181467 O Mahony Richard Mahony Kerry Kenmare R-M269

165114 Mahoney Cain Mahony; m.1821 Cork Liscleary R-L159 Table 9: O'Mahony participants in the Z255 haplogroup cluster.

This branch of the O’Mahonys centers around a single kit which has tested positive for the L159.2 SNP.

The L159.2 SNP was discovered in 2009 and correlated with an STR cluster called “The Irish Sea” cluster

for its prominence among families with origins in Leinster and the Irish Sea cost of Great Britain (Casey).

This SNP was later discovered to be downstream of the Z255 SNP (R-Z255 and Subclades). The genetic

distances between the O’Mahony participants in this cluster are quite large (from 9 to 11 at 37 markers),

so it’s difficult to predict whether all three kits in this cluster will be positive for the downstream L159.2

marker.

All three of the participants in this cluster

record a location for their most distant known

ancestor: one in eastern County Cork, one in

western County Kerry, and the last in County

Galway. This is the largest geographic spread

for a haplogroup cluster in the O’Mahony

Surname Project.

An estimate for the TMRCA gives a similarly

broad distance between the kits (Figure 14);

only kits 181467 and 165114 might share an

ancestor in a genealogical time frame. It may

be the case that these participants represent

three distinct family lines. Interestingly, there

is a McMahon cluster in the Z255 Haplogroup

Project associated with a line of McMahons

from Limerick – perhaps one or more of the O’Mahony participants in the Z255 cluster are actually

descendants of the McMahons. All three participants in this cluster should consider Family Tree DNA’s

R1b-Z255 SNP Pack or YSEQ’s R1b-Z255 Panel to determine to which branch of this haplogroup they

belong, perhaps after confirming that they are positive for the Z255 SNP first.

Figure 14: Time to Most Recent Common Ancestor for Z255 kits with 37-marker STR data.


Limitations This study is based on an incomplete dataset; were there a higher rate of recent, comprehensive SNP

testing among participants in the O’Mahony Surname Project, the dendrogram and clustering process

would not be necessary because the haplogroup of each participant would already be known. Future

SNP testing by O’Mahonys may prove that some participants do not actually belong to the haplogroup

predicted by the 37-marker STR clusters. There are also certainly other clusters in the model for which a

haplogroup could not be identified because none of the participants in the cluster had undergone any

sort of SNP testing. It is clear that STR testing alone is insufficient for meeting the goal of matching any

individual O’Mahony to a larger lineage or sept of the clan.

There are also significant gaps in the ancestral information for many members of the O’Mahony

Surname Project. Mapping the most distant known ancestor for participants that are missing ancestral

information in this study could significantly change the geographic clusters and lead to new insights on

the haplogroup clusters.

This study included all O’Mahony participants who had tested at least 37 STR markers. This induces

some sampling bias as some family lines are potentially over-represented in the data. Future studies

may benefit from limiting the samples included when multiple participants are descendants of a known

recent common ancestor.

Each haplogroup cluster has been discussed in rather broad terms, but each group merits further study.

In particular, the Kerry O’Mahonys have a number of well documented historical branches, and these

may correlate with specific subclades of the CTS4466 haplogroup, or with O’Mahonys who aren’t in one

of the currently identified haplogroup clusters.

Conclusions It is not yet possible to identify the haplogroup of Mahon mac Cian from the present data. Of the 135

participants in this study, only two provided family history information that claimed descent from an

identified sept of the O’Mahonys who descend from Mahon. These two participants belong to separate

haplogroups – FGC5494 and M222 – and thus cannot be patrilineal descendants of the same

genealogical ancestor. If, as the history claims, all Kerry O’Mahonys descend from Diarmuid Og, then this

complicates the picture further as most Kerry O’Mahonys are in the CTS4466 haplogroup, though

FGC5494, L226 and Z255 each have one participant from Kerry as well. The L226 O’Mahonys are clearly

associated with the O’Mahonys of Kilbeheny sept, but that sept’s relationship back to Mahon mac Cian

is less certain.

Sept Associated Geographically Associated by Family History

O'Mahony Fionn FGC5494, M222 M222

O'Mahony Carbery CTS4466, FGC5494, Z251, P314.2

O'Mahony of Kerry CTS4466, FGC5494, L226, Z255

O'Mahony of Kilnaglory CTS4466

Clan Fineen na Ceithirne FGC5494 FGC5494

O'Mahony of Kilbeheny L226 L226 Table 10: Summary of haplogroups associated with septs of the O'Mahony clan based on evidence given in the findings above.


However, if it can be presumed that the majority of O’Mahonys living today are descendants of Mahon

mac Cian and that Mahon lived about 1000 years ago, then only two haplogroup clusters in the

O’Mahony Surname Project fit that criteria: CTS4466b and FGC5494. Both of those clusters’ participants

are found in the lands that belonged to the Eóganacht Raithlind when Mahon became their chief and

both have a time to most recent common ancestor estimate that corresponds roughly to the time of

Mahon and his immediate descendants through Donogh na Himerce Tiomcuil O’Mahony. The CTS4466

haplogroup is common among the south Irish and the Eóganacht tribes, such as the O’Donoghues and

the McCarthys, which supports the ancient historical claim of a common descent from Conall Corc.

However, the chiefy line of the McCarthys has been shown to be part of the P314.2 haplogroup despite

the prominence of CTS4466 among their clansmen. Perhaps the O’Mahonys are similar, having a chiefly

line of FGC5494 despite many CTS4466 clansmen.

In fact, the prominence of CTS4466 in the Kerry O’Mahonys while the majority of FGC5494 is found

within the traditional O’Mahony lands may explain the dispute among the sons of Diarmuid Mor

O’Mahony. When Fineen became chief of the western O’Mahonys upon his father Diarmuid’s death, he

refused to uphold his father’s arrangement to give O’Mahony lands and castles to his younger brothers

Donal and Diarmuid Og, causing these brothers to leave for lands in north Cork and Kerry under

MacCarthy Mor. Perhaps these younger brothers were not natural sons of Diarmuid Mor – possibly sons

from a prior marriage of Diarmuid Mor’s first wife or foster sons. This might explain Finin’s reluctance to

give them the lands their father had promised them and why the FGC5494 haplogroup is found in lands

associated with the O’Mahony Fionn sept in Kilmoe and the O’Mahony Ceitherne sept in Kilmurray

(which split from the western O’Mahonys before Diarmuid Mor’s generation), while CTS4466 is found in

Kerry and north Cork, but not found in Kilmoe where the O’Mahony Fionn lived. This, though, is just one

conjecture drawn from rather incomplete data.

The present data offers some progress towards the goal of identifying specific markers to designate

septs of the O’Mahonys. The L226 and P314.2 SNPs are clearly belong to specific clusters of O’Mahonys,

and both of these groups are very close to discovering downstream SNPs that will become the identifier

for the O’Mahony lineages within these haplogroups. The Z251 haplogroup cluster, with NGS testing, is

also likely to be able to discover a SNP that is unique to this family line. The small M222 haplogroup

cluster is remarkably well associated with the O’Mahony Fionn sept. The CTS4466b cluster already has

several participants with NGS test results that make it easy for other members of the cluster to test for a

small handful of SNPs to verify their relationship to this family line.

This study should be taken as a summary of the current knowledge of the O’Mahony clan that attempts

to unite the history with the most current genetic data. It suggests an association between haplogroups

and septs of the clan, but there are large gaps in the data that make more exact conclusions impossible.

It is hoped that this study will encourage the participants of the O’Mahony Surname Project to pursue

further genetic testing and contribute to the family history research to better our understanding of this

ancient Irish clan.

Acknowledgements Finbar O’Mahony, administrator of the O’Mahony Surname Project, assisted in contacting participants of

the project. William Maney provided a wealth of information regarding the recent family history of the

M222 O’Mahony participants. Michael Mahoney and Carlos Mahoney participated in SNP testing to


assist in the identification of the FGC5494 group. John Mahoney provided some information on the Z251

haplogroup and Gwynneth Bennet, whose 2015 article called for a study incorporating the O’Mahony

DNA and historical information, communicated with me regarding the O’Mahonys of Kilbeheny.

References Bennet, G (2015) DNA is About People not Numbers, The O’Mahony Journal, 28:41-48.

Casey, R, Analysis of L159.2 SNP,

http://www.rcasey.net/DNA/R_L21/Analysis/R_L21_Analysis_L159.html, accessed 27 May 2017.

Central Statistics Office Ireland (2014) Census 2011 Boundary Files,

http://www.cso.ie/en/census/census2011boundaryfiles/, accessed 23 May 2017.

Family Tree DNA, http://www.familytreedna.com, accessed 19 Jan 2017.

Hay, M, (2017) The Atlantic Celtic branch (L21), Eudpedia

http://www.eupedia.com/europe/Haplogroup_R1b_Y-DNA.shtml#L21, accessed 23 May 2017.

Howard, WE (2009) The Use of Correlation Techniques for the Analysis of Pairs of Y-Chromosome DNA

Haplotypes, Part I: Rationale, Methodology and Genealogy Time Scale. Journal of Genetic Genealogy,

5(2):256-270.

Jost, M (2014) FGC5496 (L21>DF13>FGC5496) and Subclades. Anthrogenica,

http://www.anthrogenica.com/showthread.php?1817-FGC5496-(L21-gt-DF13-gt-FGC5496)-and-

Subclades, accessed 15 May 2017.

Maney, W (2017), letter to the author.

McCarthy, N (2016) McCarthy Groups B and K,

https://mccarthydna.files.wordpress.com/2016/12/mccarthy-groups-b-and-k-phylogenetic-tree-2016-

12-21.pdf, accessed 25 Jan 2017.

McGee, D (2008) Y-Utility: Y-DNA Comparison Utility, FTDNA Mode,

http://www.mymcgee.com/tools/yutility.html?mode=ftdna_mode, accessed 28 May 2017.

O’Brien Surname Project, https://www.familytreedna.com/groups/obrien/about/background, accessed

28 May 2017.

O’Hart, J (1892) Irish Pedigrees; or the Origin and Stem of the Irish Nation, 5th edition. James Duffy & Co.

Ltd., Dublin. Vol 1.

O’Mahony, J (1913) History of the O'Mahony septs of Kinelmeky and Ivagha. Guy & Co. Ltd., Cork.

O’Mahony Surname Project, https://www.familytreedna.com/groups/omahonysurnameproject,

accessed 19 Jan 2017.

R-M222 and Subclades, https://www.familytreedna.com/groups/r-1b-1c-7/about/background, accessed

28 May 2017.

R-Z251 and Subclades, https://www.familytreedna.com/groups/r-z251/about/news, accessed 28 May

2017.

http://www.rcasey.net/DNA/R_L21/Analysis/R_L21_Analysis_L159.html

http://www.cso.ie/en/census/census2011boundaryfiles/

http://www.familytreedna.com/

http://www.eupedia.com/europe/Haplogroup_R1b_Y-DNA.shtml#L21

http://www.anthrogenica.com/showthread.php?1817-FGC5496-(L21-gt-DF13-gt-FGC5496)-and-Subclades

http://www.anthrogenica.com/showthread.php?1817-FGC5496-(L21-gt-DF13-gt-FGC5496)-and-Subclades

https://mccarthydna.files.wordpress.com/2016/12/mccarthy-groups-b-and-k-phylogenetic-tree-2016-12-21.pdf

https://mccarthydna.files.wordpress.com/2016/12/mccarthy-groups-b-and-k-phylogenetic-tree-2016-12-21.pdf

http://www.mymcgee.com/tools/yutility.html?mode=ftdna_mode

https://www.familytreedna.com/groups/obrien/about/background

https://www.familytreedna.com/groups/omahonysurnameproject

https://www.familytreedna.com/groups/r-1b-1c-7/about/background

https://www.familytreedna.com/groups/r-z251/about/news


R-Z255 and Subclades, https://www.familytreedna.com/groups/r1b-l159-2/about, accessed 27 May

2017.

R1b-CTS4466 Plus Project, https://www.familytreedna.com/public/R1b-CTS4466Plus/, accessed 25 Apr

2017.

Sayers, B (2005) The O’Mahonys of Kilbeheny and the 1798 Rising, The O’Mahony Journal, 27:3-13.

Townlands.ie database, http://www.townlands.ie, accessed 13 Apr 2017.

Trinity College Dublin (2013) The Down Survey of Ireland, http://downsurvey.tcd.ie/index.html,

accessed 23 May 2017.

Williamson, A (2017) The Big Tree, http://www.ytree.net/, accessed 25 May 2017.

YFull, YTree v5.03, https://yfull.com/tree/, accessed 25 Apr 2017.

https://www.familytreedna.com/groups/r1b-l159-2/about

https://www.familytreedna.com/public/R1b-CTS4466Plus/

http://www.townlands.ie/

http://downsurvey.tcd.ie/index.html

http://www.ytree.net/

https://yfull.com/tree/

the o’mahonys - cai mavercaimaver.com/mahoney/dna-paper/the-omahonys-paper_maver_2017.pdf · the...

Documents