One of the largest groups on the Fitzpatrick DNA study has many members who trace to Ossory, and of all the major DNA groups their roots are perhaps the most complex to understand. They are readily identified by unique sets of Y-STR markers, most notably DYS390=21 and YCAII=22-23, which afford the easy identification of haplogroup A1487, a young sub-group of FGC5494. The arrival of those considered as bearing the DNA signatures the early Irish Celts is considered to have been in ancient times, ca. 2500-2000 BC. FGC5494 is clearly distinct in this regard because its recent continental origins are well documented. However, a large block of more than 20 SNPs that includes A1487 is one of the few distinctly Irish sub-groups of FGC5494.
A1487 is represented by some of the greatest surnames in Irish history; at FTDNA there are Fitzpatricks, FitzGeralds, D’Altons and Brennans who are proven A1487. Other surnames that have close Y-STR matches with A1487 men at FTDNA include those with Irish or Norman surnames, but still the most common are those four; a note of caution is warranted at this stage. Just because a surname dominates a particular haplogroup doesn't mean it is the founder or progenitor. Nevertheless, key to understanding the shared origin of these three great clans is the age of A1487, and that of his immediate genetic relatives; his father, his siblings and his children.
The Fitzpatrick Barons of Ossory, starting with Barnaby Fitzpatrick, claimed descent from the Mac Giolla Phádraig dynasts, but the Frankish roots of his descendants makes direct paternity from the ancient chieftains untenable. This should not shock or surprise because it is well understood that genealogies cannot always be relied on. Throughout history there have been many occasions when they have been manipulated to, in the words esteemed Irish historian Professor Donnchadh Ó Corráin, “re-interpret the past in the interest of the contemporary socio-political structures and power-holders”.
So what can we discover about the arrival of A1487 in Ossory? By analysing the Y-DNA 67-marker data of approximately fifty A1487 men, mostly with the surnames Brennan, D'Alton, FitzGerald or Fitzpatrick, along with A1487 siblings and cousins it is possible to derive a modal haplotype for A1487. Calculation of the TMRCA (time to most recent common ancestor) for the group, in conjunction with SNP age analysis, leads to A1487 being from
ca. 750-1050 AD. Hence, it is likely A1487 was also Frankish by birth and either he, or his not too distant descendants probably landed in Ireland in the late 12th Century.
The present day names of the cousins of A1487 Fitzpatricks read like a medieval Who's Who of the rich and famous; they are names associated with some of the most powerful overlords in Irish history.
The presence of these Cambro-Norman Lords was first felt in Leinster right from the onset of the invasions of Ireland in the late 12th Century.
One of most influential FitzGeralds during the latter stages of the kingdom of Osraige was Margaret FitzGerald, Countess of Ormonde, daughter of Gerald FitzGerald (8th Earl of Kildare) and wife of Piers Butler (8th Earl of Ormonde). Their daughter, Margaret Butler, married Barnaby Fitzpatrick the 1st Baron of Upper Ossory ca. 1532.
Sir Walter D'Alton, an Anglo-Norman knight, is recorded as landing in Ireland in 1173 AD and his descendants became Governors in County Meath.
Writing in his 'History and Antiquities of Kilkenny', Healy maintains it was the strong relationship the D'Altons had with the Kildares that led to their introduction to County Kilkenny by the Earls of Ormonde in the mid-16th Century, although their presence has been noted being from the late 14th Century when William D'Alton was appointed Keeper of the Peace in Kilkenny.
Well intertwined with the Fitzpatricks of Ossory were the Brennans, with all things familial between the two clans being too many to number.
O'Hart's 'Origin and Stem of the Irish Nation' details two particularly notable marriages between the clans. First, between Dermod Reagh O'Brenan (a 14th Century Prince of Idough) and a daughter of Geoffrey Fitzpatrick, King of Ossory and, second, between John O'Brenan and a daughter of Callough Fitzpatrick an illegitimate son of Barnaby Fitzpatrick, 1st Baron of Upper Ossory.
Notwithstanding the ancient link between the first Giolla Phádraig and the first O'Braoinan (who was his grand uncle), based on DNA evidence that relationship is around 300-500 years too early and it doesn't readily explain the A1487 Norman fingerprint. Whatever secrets lay between the bedsheets of the Fitzpatricks, Brennans, D'Altons and FitzGeralds, they are laid bare by DNA. Can it be a mere coincidence that the closest match to the 'primordial' DNA signature of the common ancestor of A1487-Fitzpatricks-Brennans-D'Altons-FitzGeralds is a man with the surname Butler? Critique the DNA evidence for yourself, it's presented in the A1487 TMRCA Matrix and Haplotree.