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McGrath Project
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An Analysis of the McGrath Clan Project Big-Y Results


In an important sense, Y-genetic science as we pursue it at FTDNA is precise. It's about a very real entity, the Y-chromosome comprised of distinct units as it's passed down, largely unchanged in a population from father to son. But sometimes mutations, tiny changes, occur in the passing. These mutations are distinct events, and when they occur a fork or branch occurs.  Going forward, we have two versions of the Y-chromosome in the population instead of one. With time, those versions may well branch again as further variations occur, passing the chromosome from father to son. For a particular population, those collective branches can be represented as a “genetic tree”, not unlike the descendant tree we are more familiar with in traditional genealogy.  There are, however, some important differences between the two types of trees.

The purpose of either a descendant tree or a genetic tree is the same – to trace lineages and show relationships back to a common ancestor. However, instead of showing “parent-children” relationships, a Y-genetic tree shows “father-son” relationships. Moreover, since mutations of the Y-chromosome only occur, on average, every 80 years or so, not every generation is represented.

Although a mutation is a precise event and occurs at a particular time and with a particular individual, we will almost never know that individual by name. Still, we give the individual a code name, say “FTC87759.”   And while we may not know the precise date when a particular branch occurred, we can nevertheless estimate it, sometimes rather closely. 

With this brief background in mind, the next section describes a genetic tree that was constructed for the McGrath Clan DNA project.

Genetic (SNP) Tree

(Click here to view a downloadable image file)

This chart is based on member kits in our McGrath project that are positive for the major haplogroup R1b, are downstream of R-M269, have been analyzed for Big Y-700 and meet one of the following criiteria:

1. EKA surname is a variant of "mac Craith", irrespective of terminal haplogroup; or

2. Terminal haplogroup is R-L226 (Dál gCais) or R-M222, irrespespective of the EKA surname 

The Big Y test examines the Y-chromosome for mutations known as “single nucleotide polymorphisms” (SNPs) and these mutations, identified by an alphanumeric code, are plotted against their known estimated age.  Each kit is shown along the bottom of the diagram and are identified by their kit numbers along with their earliest known male ancestor (EKA).


The tree addresses three key questions. How did this arrangement of kits come to evolve from R-M269 and the most recent common ancestor we had prior to about 2500BC when the first distinct branch occurred during the early Bronze Age in Eastern Europe. What subsequent specific branches must have formed? And when, roughly, would they have had to occur?” The total span of time represented on the diagram is worth considering, roughly 6000 years from the Mesolithic Age to the present day.

Because of our shared surname, variants of mac Craith, there's a natural predisposition to suppose we might also have a shared history, perhaps some proto-Clan-McGrath founded in the mists of Ireland's Gaelic past. But the analysis does not support that simple model.

The most important genetic distinction that bears on our project membership is that between haplogroup R-M222, concentrated in the north of Ireland and includes Groups II - IV on our chart, and the “Dalcassian” haplogroup R-L226, more broadly distributed around Limerick and south, and represented by Group VII  on our chart. And this genetic split, which involved a series of mutation events, occurred before the year 0 AD.  

Importantly, the analysis confirms a significant split in the R-M222 haplogroup: an S588 subclade that led to a cluster of McGraths in Ulster, who are descendants of Eoghan mac Néill of Co. Donegal.  This S588 subclade appeared centuries before Clan McGrath activities in the Termon Magrath area around Lough Derg and Pettigo, and there is no evidence of social interaction with them. It's probable that they arrived at the McGrath surname independently.  

Our study makes clear that, even within the broad R-M269 haplogroup, our McGrath heritage and genealogy has been complex for a long time. Our history is not that of a monolithic genetic clan.

Nor in real life were individual clan groups monolithic. If social systems, such as clans, had the precise edges of genetic haplogroups, it might suggest a clean split between the Ulster and Dalcassian septs.  And, to be sure, we can be confident that the Ulster McGraths of clan days had a concentration of M222, and the Dalcassian McGraths a concentration of L226.  But the clans were social systems and so had imprecise edges that were porous and changed with time. Individuals and families moved about a bit, or even a lot. Individuals were surely adopted into a clan sept for various reasons. Invasions (such as the Vikings and Normans) and inter-clan battles would have disturbed boundaries and created some social mixing. And of course, elicit love can always play a role.

With respect to famous individuals associated with Clan McGrath,  one of our kits, #29355, is a direct descendant of Brian Boru (941-1014), whose brother was the progenitor of the Dalcassian sept of Clan McGrath which, of course, then has its origins in that remote time period.   We believe another of our kits, #684718, is a direct descendant of the noted and controversial Archbishop Miler Magrath (1522-1622), whose life coincided with the end of the Termon Magrath sept and the onset of the Ulster Plantation.

In closing...

If your kit is not included here, and your terminal haplogroup is R-M269, what does this study mean to you?  Unfortunately very little, other than your kit is typical of the majority of Western European men. 

We can use your STR results from the Y-67 and Y-111 tests to predict whether your kit is positive for R-M222 or R-L226, but they are only just that - predictions. Moreover, while these tests can be helpful in confirming patrilineal relationships or validating paper records, they are not particularly useful for identifying more distant ancestral connections.

In order to gain the resolution necessary to identify genetic relationships beyond paper records and learn more about your patrilineal heritage, you will need to upgrade your kit to the Big Y-700 test. These upgrades are less expensive than a standalone Big Y test, the cost of which may be beyond your current budget.  For example, if you upgrade from the Y-111 test, there is an almost 50% discount from the full price. Other options, such as cost-sharing between family members, can also help to reduce the financial burden even further.

If you are interested in upgrading to Big Y, but are unsure of how (or if) you might benefit from your investment, feel free to ask for advice and support using our project's Activity Feed. 

Last updated: 9 November 2022