Below is an analysis of each of the genetic groups identified within the project ... so far. Additional groups will be discovered over time.

An explanation of the methodology used for grouping people into different groups can be found in this blog post here. In brief, people are grouped together if they are likely to have a common ancestor within the last 1000 years (i.e. since the origin of surnames in Ireland and the UK).

Group 1a - the O'Reilly Clan of Cavan

People within this group have either been placed here based on their SNP results (via Big Y usually) or because they are a very close STR match (i.e. Genetic Distance  2/37, 4/67, 5/111) to someone who has done SNP testing. People in this group belong to Haplogroup R1b and sit on the branch of the Tree of Mankind characterised by the upstream SNP marker M222 (which arose about 2000-4000 years ago, probably in Scotland or Ireland). Several other groups share this upstream SNP marker, but Group 1a has been further characterised by the presence of the downstream SNP marker BY21239 (which is about 500-1000 years old). So the SNP Sequence (i.e. list of ancestral SNPs) associated with this branch is as follows:

• R-M222 > S658 > DF104 > DF105 > A18726 > A259 > A260 > BY3338 > BY11723 > A883 > A885 > FGC37744 > A887 > BY21239

In addition, there are several sub-branches below this, as follows:

• BY21239 > Y54272 > FT390508
• BY21239 > Y131835 > Y131834
• BY21239 > FT375780
• BY21239 > FT128962

The Big Y Block Tree indicates that this SNP marker (BY21239) is associated primarily with people named Riley, Reilly, or O’Reilly and may thus be a SNP marker that arose in the founder of the surname. If this is so, then the sub-branches would be various branches of the larger Riley “clan” that arose over the last 1000 years. 

Group 1a is the largest of the genetic groups (representing about 17% of Y-DNA tested Riley’s in the project). Of the 20% of group members who have reported a birth location for their MDKA, in 56% of cases this was in county Cavan and 33% in the adjacent county Meath. It is therefore highly likely that this group represents the descendants of the O’Reilly clan described by Woulfe in his Irish Names & Surnames (1923):

The O'Reillys, who are the same stock as the O’Rourkes, were chiefs of Breifney-O'Reilly, which originally comprised the greater part of the present Co. Cavan. In the course of the 13th and 14th centuries they became very powerful and extended their dominion over the whole Co. Cavan and parts of Meath and Westmeath; and they were sometimes chiefs of all Breifney. They maintained their independence as a clan down to the time of James I, and continued in possession of considerable property until the Cromwellian confiscations. Many of the O'Reillys attained to high ecclesiastical rank, no fewer than five of the name having been Primates of Armagh. The name is now one of the most common in Ireland, but owing to its numerous dialectical variations is variously anglicised in different parts of the country.

Over time, it may be possible to associate the downstream branches below BY21239 with specific historical branches of the O’Reilly clan, such as the O’Reilly’s of Dromore, or of Drumgora, or of Corlattylannan. This will depend on project members supplying their MDKA birth locations and pedigrees (via the Activity Feed) as well as more Big Y data.

Group 1f (possibly Irish or Scottish)

In May 2021, I moved new member 951783 into the same group as 4 other family members, all of whom share the same MDKA, namely Jonathan Riley 1818-1880, Clay county, Illinois.

Looking at his STR matches, we can see the major problem that many people face if they sit on the M222 branch of the Tree of Mankind. This particular Y-DNA signature is so common that he has over 1800 matches at the 37-marker level of comparison. This clearly indicates that a lot of these matches are going to be chance matches / false positive matches. We can recognise the ones that have different surnames as being probable chance matches (barring the occasional NPE / surname switch), but the ones that are called Riley (or similar) could EITHER belong to the same group (i.e. Group 1f) or to one of the other Group 1 subgroups. And that’s the problem - unless they upgrade to the Big Y test, we cannot be sure of their correct allocation to a specific subgroup.

For example, this new member (951783) matches several other Riley’s within the project, but some of these definitely sit on completely different branches of the Tree of Mankind (we can tell from their SNP results). Here are the SNP Sequences of two other Riley’s that he matches at a Genetic Distance (GD) of  4 / 37 … without SNP testing (e.g. Big Y), we would not have been able to tell which of these groups they belonged to:

• M222 > S658 > DF104 > DF105 > A18726 > A259 > A260 (Groups 1a, 1b, 1c, 1d)
• M222 > S658 > DF104 > DF105 > A18726 > A259 > A260 > BY3338 > BY11723 > A883 > A885 > FGC37744 > A887 (Group 1a)
• M222 > BY35297 > FGC4077 > A725 > FGC40940 > FGC40947 > FGC40949 > BY35282 (Group 1f)

The common ancestor for all these groups is M222 which arose some 2000-4000 years ago, well outside the timeframe of surnames.

Luckily, in the case of 951783, several of his close cousins have done Big Y testing and this known genealogical relationship and his very close STR match to them (GD = 0/37) allows us to group him with them in Group 1f.

Group 1 (probably Irish)

This group is for those project members who sit on the M222 branch of the Tree of Mankind but who have not done sufficient additional SNP testing to allocate them to a particular subgroup of Group 1 (there are 5 currently). These people will need to do Big Y testing in order to be appropriately allocated to their relevant subgroup.

Group 3 (an isolated branch)

This group belongs to Haplogroup R1b and sits on the branch of the Tree of Mankind characterised by the SNP marker FT285531 (which arose about 800-2400 years ago, somewhere in the UK possibly). The SNP Sequence (i.e. list of ancestral SNPs) associated with this branch is as follows:

• R-P312 > DF19 > DF88 > FGC11833 > S4281 > S4268 > Z17112 > S17075 > S10067 > Z17115 > FT66914 > FT285531 > FTA30093 
• … additional sub-branches may be identified as more people undertake the Big Y test

A (crude) visual representation of the path of migration of this particular group into Europe can be found on the Scaled Innovation website here.

The Big Y Block Tree shows that this group sits on a relatively isolated branch of the Tree of Mankind and they share a common ancestor with their nearest genetic neighbours about 2400 years ago.

Group 13 (possibly Scottish; previously McDonald or Dundas?)

This group belongs to Haplogroup R1b and sits on the branch of the Tree of Mankind characterised by the SNP marker BY3249 (which arose about 500-1500 years ago, probably somewhere in the UK or Ireland). The SNP Sequence (i.e. list of ancestral SNPs) associated with this branch is as follows:

• R-L21 > S552 > DF13 > DF21 > Z16267 > F24434 > Z3000 > Z3006 > Z3008 > S953 > ZZ13_1 > FT14481 > A938 > FT112238 > BY3249

A (crude) visual representation of the path of migration of this particular group into Europe can be found on the Scaled Innovation website here.

The Big Y Block Tree shows that this group sits on a branch of the Tree of Mankind where the dominant surname (on this and surrounding branches) is McDonald. This strongly suggests a Scottish origin for this genetic group.

It is possible that there was a Surname or DNA Switch somewhere along this line, probably from McDonald or Dundas to Reilly. If this is the case, the switch probably occurred some time before 1850 (based on a GD of 4/111 to another Reilly).

Group 17 (possibly Scots-Irish; previously Burns or Fuller?)

Big Y results for member 921735 identified additional ancestral SNP markers for Group 17. We already knew that the people in this group belonged to Haplogroup I and sat on the branch of the Tree of Mankind characterised by the SNP marker M223 (which arose about 17,000 years ago in central Europe). But the new results move this group 14 branches further downstream to branch MF25261 (which is about 500-1000 years old). So now, the SNP Sequence (i.e. list of ancestral SNPs) associated with this branch is as follows:

• I-M223 > P222 > CTS616 > FGC15071 > M284 > L1195 > L126 > FGC20063 > FT2393 > S7753 > Y4142 > Y4751 > BY3610 > Y63570 > MF2526

A (crude) visual representation of the path of migration of this particular group into Europe can be found on the Scaled Innovation website here.

Member 921735 shares this new “terminal SNP” (i.e. MF25261) with someone called Armstrong, and adjacent branches on the Tree have people called Burns & Byrne. Also, this member has STR matches with people called Burns, Fuller, Robertson, and MacDonald, as well as Riley. So there is a sense that the genetic origins of this particular group may be Scottish. This is consistent with the MDKA information supplied by two of this groups members, which indicates origins in Northern Ireland, suggesting that this group may be Scots-Irish. It is possible that a Surname or DNA Switch (e.g. from Burns or Fuller to Riley) occurred somewhere along the line, but (given the Genetic Distance of 4 / 67 among members of this group) such a switch probably happened some time before 1850.

ANALYSIS OF ADDITIONAL SUBGROUPS WILL BE ADDED OVER TIME.

Maurice Gleeson
Last updated: May 2021