Taranis
Elite member
I2a-Isles has a center of diversity that spans both Britain and Ireland, seeing that all of its main STR clusters are present in both places, so we can't place its MRCA location very precisely, but we can be fairly sure that he was insular. The TMRCA of I2a-Isles makes it perhaps the best candidate for the status as the dominant haplogroup of the Grooved Ware peoples. That means that, as a clade, it spans the different ethnicities of the British Isles, and determining which particular ethnicity your I2a-Isles line passed through will need to utilize STR comparisons (as you're already doing, good job).
It would actually be very interesting if I2a2b in Ireland is really derived from the Grooved Ware Culture. I mean, if this is the case then it's clearly pre-Indo-European, and would as such obviously predate the emergence of all historically known ethnicities of the British Isles.