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Edwin B. O'Neill



The purpose of this document is to explain in non-technical terms the use of DNA in O'Neillgenealogy and in the history of the O'Neills of Ireland. SOME OF WHAT FOLLOWS IS THE JUDGEMENT OF THE AUTHOR, SUBJECT TO CHALLENGE BY ANY AND ALL.


Background O'Neill History

Recorded history says there was a man, Niall Noigiallach, more commonly known as Niall of the Nine Hostages, who established a dynasty in Ireland that lasted many centuries. Niall, who died in the year 405, was the 127th King of Ireland. He lived over 500 years before surnames (such as O'Neill) came into existence. Niall's dynasty was called the Ui Neill (pronounced ee-neel).

Later history also records that after surnames had begun to be used, men with many, many surnames (such as Ryan, O'Sullivan, Kennedy, Byrne, O'Donnell, McLaughlin, etc.) were direct descendants of Niall of the Nine Hostages. In addition it records that the Royal Tyrone O'Neills of Ulster, who were kings or rulers of part or all of Ireland for about 650 years, were also descended from him.

Niall Glundubh, 170th King of Ireland (916-919), historically identified as a descendant of Niall of the Nine Hostages, is the namesake of the O'Neills. His grandson, Domhnall of Armagh, 173rd King of Ireland (956-980), was the first to use the surname that became O'Neill. He took the name, Domhnall Ardmacha Ua Neill (Donald of Armagh O'Neill). Ua Neill is pronounced oo-ah-neel. Niall, Domhnall and the kings that followed them were located in the Province of Ulster.

In addition to these Royal Tyrone O'Neills of Ulster, history records the existence of several other O'Neill septs that were probably not related to the Ulster O'Neills. These include the O'Neills of Magh da Chonn (the same as the Carlow O'Neills) centered in the counties of Waterford, South Tipperary and Carlow, and the Thomond O'Neills, centered in counties Clare, Limerick and north Tipperary.


DNA 101

In the cell of a male human being there are X- and Y-chromosomes; females do not have Y-chromosomes. Through use of powerful "microscopes" scientists have identified specific locations within the Y-chromosome of males and have named each location (such as DYS 391, DYS 19, etc., where DYS means DNA Y-chromosome Segment). These locations are called markers or loci. In a typical Y-DNA test (DNA in the Y-chromosome) 25 markers are used and, at each marker, the number of a specific pattern is counted and the overall results tabulated, such as:


DYS393 390 19 391 385a 385b 426 388 439 389-1 392 389-2 458 459a 459b 455 454 447 437 448 449 464a 464b 464c 464d


These indicate there are 13 of the particular pattern at Marker DYS393, 24 at Marker DYS390, etc.

What is significant about the Y-DNA results as tabulated is that, in almost all cases, a father passes his Y-DNA onto his son unchanged (the tabulated values for the father and son are identical at all markers). If a father always passed on his Y-DNA to his son then any patrilinear descendant (male to male to male. etc.) of Niall of the Nine Hostages would have the same Y-DNA. But the actual situation is that occasionally the Y-DNA changes (mutates) between a father and son.

Experimentally it has been determined that, for a 25 marker test, on an average each marker will change/mutate once approximately every 360 generations[1]. But, since we test at 25 markers, one of the 25 markers will, on average, change every 360/25=14.4 generations, or approximately every 430 years.

Taking this a step farther, if we have two O'Neills who are Y-DNA-tested at 25 markers, the ancestors of each one will have experienced, on average,one marker change in 430 years so the two together will have seen two changes in 430 years or an average of one difference between them every 215 years. So, for instance, if the two O'Neills are Y-DNA tested and they differ at three markers, the most likely outcome isthey have a common ancestor within the last 645 years. This common ancestor is called the Most Recent Common Ancestor (MRCA). I stress these are only statistical numbers and should be used only as general guidance.

Based on Y-DNA tests, it is possible conclusively to say that two O'Neills are NOT related. Or to say they are related and approximately how far back one must go to find the MRCA.

The above example assumed testing at 25 markers but many have chosen to be tested at 37 or 67 markers and here the precision becomes better. For instance, for two O'Neills tested at 37 markers that differ at one marker, the likely MRCA is about 80 years or sooner and for 67 markers it's 65 years or sooner. Again it is cautioned that these are statistical numbers and, hence, only "the likely MRCA".


O'Neill History and DNA

As mentioned above, persons with many surnames are historically linked as descendants ofNiall of the Nine Hostages. From Y-DNA testing today of persons bearing these numerous non-O'Neill surnames many have DNA very similar to one another. Their most common DNA "signature" is:


DYS393 390 19 391 385a 385b 426 388 439 389-1 392 389-2 458 459a 459b 455 454 447 437 448 449 464a 464b 464c 464d


Since these surnames have DNA similar to one another and since they are all, by history, descendants of Niall of the Nine Hostages, it is reasonable to assume this "signature" represents the DNA of Niall of the Nine Hostages (Ui Neill). This "signature" is called the Ui Neill haplotype.

As of the datethis document was initially drafted the Y-DNA measurements of over 145 O'Neills had been recorded but only 15 (about 10%) appear to show the Ui Neill haplotype. These 15 are predominantly in Ulster Province, the location of the Royal Tyrone O'Neills.

A much larger number of the 145 O'Neills, 51 (35%), also predominantly in Ulster Province, possess an entirely different Y-DNA haplotype, as follows, those markers highlighted in red being those differing from the Ui Neill haplotype:

DYS393 390 19 391 385a 385b 426 388 439 389-1 392 389-2 458 459a 459b 455 454 447 437 448 449 464a 464b 464c 464d

1324 141112151212111313301791011112515193015151717

The author has labeled this haplotype the O'Neill Variety; the author has Y-DNA very similar to the O'Neill Variety haplotype. Because the O'Neill Variety haplotype differs so greatly from the UiNeill haplotype, it is clear they are not related and persons who test O'Neill Variety are, in the opinion of the author,not descendents of Niall of the Nine Hostages.

As documented in a paper the author co-authored,, there is strong evidence to suggest the original Royal Tyrone O'Neills of Ulster (starting with Domhnall Ardmacha Ua Niall) were descended from Niall of the Nine Hostages and those 10% of O'Neills in the DNA database with Ui Neill haplotypes are descended from that Royal O'Neill line. There is also strong evidence that, at some point in time, the Royal O'Neill line was continued by someone who was not one of the original Royal O'Neills and the 35% of O'Neills with O'Neill Variety haplotypes are descended from that later Royal O'Neill line. Since the O'Neills were kings or rulers during the era of both the original and the later Royal O'Neill, both lines would represent Royal Tyrone O'Neill lines.

It is also noted that more than half of the O'Neills tested had Y-DNA "signatures" that were neither Ui Neill nor O'Neill Variety.

Recently, evidence has started to emerge suggesting possible linkage of Y-DNA results to the O'Neills of Magh da Chonn (the Carlow O'Neills). The evidence is based on the opinion of a noted O'Neill researcher, Sean O'Neill begin_of_the_skype_highlighting     end_of_the_skype_highlighting, who published a book[i] on the origins of this O'Neill sept and who believed two of those who had been Y-DNA tested were from that sept. If true this evidence suggests the O'Neills of Magh da Chonn are a completely separate sept from the Ulster (Tyrone) O'Neills. With differences from the Ui Neill Variety shown in red and differences from the O'Neill Variety in blue, the tentative haplotype for the O'Neills of Magh da Chonn is:


DYS393 390 19 391 385a 385b 426 388 439 389-1 392 389-2 458 459a 459b 455 454 447 437 448 449 464a 464b 464c 464d

Magh da Chonn13241411111412121214 13301791011112515182915151718

Ui Neill Variety1325141111131212121314291791011112515182915161617


Magh da Chonn132414111114121212 14 13301791011112515182915151718

O'Neill Variety13241411121512 12111313301791011112515193015151717



Three different haplotypes, representing three separate and distinct genetic lines of O'Neills have been identified from Y-DNA testing. From these results the author believes it is possible to assign man-tested O'Neills to one of three categories of O'Neills: (1) Original Royal Tyrone O'Neills of Ulster, descended from Niall of the Nine Hostages (Ui Neill); (2) Later Royal Tyrone O'Neills of Ulster, descended from later Royal O'Neills (O'Neill Variety); and, (3) O'Neills of Magh da Chonn, probably descended from a separate Domnall Ua Neill (unrelated to the Ulster O'Neills), who is known to have lived in Carlow in the 9th and 10th century.

So far no DNA pattern has been discovered identifying the Thomond O'Neills or any other sept or clan despite the fact that over 50% of O'Neills who have been DNA-tested do not appear to fit the UiNeill, O'Neill Variety or O'Neills of Magh da Chonn haplotypes.


[1] There are many different estimates of the number of years associated with marker mutations/changes. The numbers used in this document came from John Chandler, one of the most knowledgeable in the area. Even though the text of this document refers to "average", the numbers are, in fact, "most likely".

[i] The O'Neills of Leinster: an investigation into the origins of the O'Neills of Magh Dachonn - Mayacomb, Leinster. Sean O'Neill. Dumnurry, Belfast, Northern Ireland: Irish Heritage Association, 1992.