Another nail in the coffin of the Iberian Irish myth
Within the last few months, the genetic genealogy community has placed a new SNP (L21 / rs11799226) on the Y chromosome phylogenetic tree downstream of the most frequent western European haplogroup (R1b). Preliminary results suggest the overwhelming majority of Irish R1b carry the mutation, while L21 is absent in the Iberian samples and subclades tested so far. R1b from England and continental northwestern Europe seem to be split between L21-derived and L21-ancestral. It's still early and I'd like to see more data, but I think L21 (and thus the direct male ancestor of the majority of the Irish) most likely originated in northwestern Europe. The supposed link between the Irish and Iberians was built on the high frequency of R1b Y-DNA in both regions. The autosomal and mtDNA data never supported any sort of special or close relationship between "Celts" and Basques; it's now clear that Y-DNA doesn't, either.