What can Y-DNA Results tell us?

Most people who join surname projects (like the O'Malley DNA Project) start off with the Y-DNA-37 marker test. This tests 37 STR markers, and you can later upgrade to 67 or 111 STR markers. Some people also do SNP marker testing, either via a special "SNP Pack" or the Big Y test. So there are two types of DNA markers - STR markers and SNP markers. You can read more about them here.

Each type of marker gives different kinds of information. The SNP markers help define the exact location that someone sits on the Tree of Mankind, whilst the STR markers give an indication of how closely two people are related within the last several hundred years. Both types of marker can provide crucial information that helps the interpretation of the overall data and allows us to draw specific conclusions about each of the genetic groups within the project.

But DNA data is not the only type of data that we analyse. We also analyse the direct male line pedigrees that project members have provided, and in particular the birth location of each MDKA (Most Distant Known Ancestor).

On an individual level, a simple Y-DNA-37 test may help you identify people to whom you are closely related. An exact match at 37 markers (i.e. no mutations; Genetic Distance = 0/37) suggests that you and the other person have a 50% chance of being related on your direct male line within 5 generations and a 95% chance of being related within 8 generations. The probabilities are even stronger for an exact match at 67 markers (50% probability within 3 generations, 95% probability within 5 generations) and 111 markers (3rd cousins or closer). Thus your own individual Y-DNA results can help you with your personal family tree research.

But you get additional value from your Y-DNA results by joining DNA projects - surname projects, haplogroup projects & geographic projects. And at this project level, your Y-DNA results can tell us a lot about the deeper origins of your specific genetic group. Here's how ...

In most projects, distinct genetic groups can be identified from the DNA data. These are groups of people who all share a broadly similar genetic signature, suggesting that they all descended from the same common ancestor some time in the last 1000 years or so (i.e. "within a genealogical timeframe", or "since the advent of surnames"). The key questions that we can ask about any genetic group within a project are:

• Where are they from?
• How old is the group?
• Is the group associated with a specific Irish "clan"?

And as the Y-DNA database has grown, various DNA projects have indeed been able to identify the genetic signatures of specific Irish "clans", thus connecting people with their deeper Irish roots and a history that few may have imagined.

Brian Boru (941-1014), High King of Ireland 

One of the earliest examples of this is the O'Brien DNA Project. The Administrators of this project worked closely with Haplogroup Project Administrators to identify a specific signature for the "tribe" of the Dal gCais (pronounced Doll Gash), one of whose most famous descendants was Brian Boru, 1st High King of Ireland, who was killed at the Battle of Clontarf in 1014. [1] The evidence collected in support of this conclusion (that a specific signature is that of the Dal gCais) includes the following:

• a specific Y-DNA signature (called the Irish Type III STR signature, which is associated with the L226 SNP marker) is in turn associated with: 

1. a significant surplus of Dal Cassian surnames (e.g. O'Brien, Casey, McGrath, Hogan, etc)
2. a higher frequency in the clan territories of the Dal gCais (centred around Clare & Limerick)

• Sir Conor O'Brien shares the same specific signature (he has a 32-generation direct male line pedigree going back to Brian Boru)

Distribution of L226 is strongest in Dal gCais territories

So Y-DNA results can help you identify matches with whom you share a fairly recent common ancestor (on your direct male line) and can link you up to the deeper origins of your surname and where it came from. This can be particularly helpful for descendants of the Irish Diaspora, many of whom do not know from which part of Ireland their ancestors originated. Knowing the deeper ancestral locations of your surname can be a starting point for focussed documentary research.

We will see in subsequent posts how the deeper origins of the various groups within the O'Malley DNA Project are coming close to identifying specific DNA signatures of specific O'Malley "clans". One group shares a probable connection to Grace O'Malley (the Pirate Queen), and another shares a connection to Brian Boru.

Maurice Gleeson

May 2019

References:

[1] Dennis M Wright, 2009. A Set of Distinctive Marker Values defines a Y-STR Signature for Gaelic Dalcassian families. Journal of Genetic Genealogy, 5(1):1-7. Available at http://www.jogg.info/pages/51/files/Wright.pdf