DNA

Neutronale

Just looking at some DNA maps of Europe. I know this is a complex area and I won't claim to understand too much, hence this thread.

What I have learnt is that the R1b haplogroup is strongest represented in Ireland and is less represented the futher east you go in Europe. The R1a hg is strongest in Eastern Europe and is less represented the further west you go in Europe.

The E3b hg and the J2 hg are among the oldest hg markers in Europe dating back to the paleolithic era and are strongest represented in Greece. They are represented at about 2% each in Ireland.

So far so good

M253 is I1, and M223 is I2b1. M423 is I2a2, and it played a substantial role in the spread of the Mediterranean wave of the Neolithic (agriculture) from its home near the Black Sea.

Consider this map of hg I2b1. Note that M253 and M423 are represented at about 10% in distribution in Connacht and has insignificant distribution elsewhere. What is the significnce of this? It is west of the Shannon and the historical record has it that during the 17th century people were forced "to hell or to Connacht", is there a correlation between these two records?

Similarly in Wales and Cornwall, there is insignificant representation in distribution of I1 and I2 almost exactly at the borders of those areas; what is the significance of this?

Neutronale

Distribution of haplogroup I1
I1 is believed to have originated in Denmark, approximately with the Nordic Bronze Age, and spread with Germanic waves of migration after 500 BC. All of its current distribution can be explained by known Germanic and Norse migrations.

A genetic marker distributed by the Vikings as far as I can make out. It seems to show that genetically the vikings left an insignificant mark on the Irish genetic lanscape, a mere 5% in the Leinster region only...Limerick will be disappointed

Ipso

The terminology in your map is out of date, this article might give a clearer picture.
http://www.buildinghistory.org/distantpast/haplogroupi.shtml

The Connacht haplogroups may represent an older lineage than R1b, apparently it urns up particularly in surnames O'Driscoll, O'Grady and possibly Keane.
I1 would most likely be from Vikings, there are a few forms of M223 which could be an early arrival post ice age or from any movement from the continent. There are a couple groups called M284 and L126 that most likely arrived from Scotland.
The I haplogroup is thought to be possibly the oldest in Europe, a recent study in the UK found that men carrying it have a higher risk of heart disease than men falling under other haplogroups.
M253 is actually part of I1, M423 would be the one that turns up in the surnames I mentioned.