I have added mtDNA frequencies for the Basques, based on this study featuring 615 samples. The Basques stand out from the rest of Europe by their exceptionally high frequency of haplogroup H (61.5%, including 44% of H1 and H3) and Europe's lowest percentage of haplogroup T (1%). They only have 2% for IWX combined, which is also the lowest frequency in Europe. This indeed suggest a very limited influx of maternal lineages from the Caucasus (where X might have originated), as well as the North Caucasus and Pontic-Caspian steppes (where W and T are especially common). Unfortunately I don't have the breakdown of U subclades, but I expect to find very little if any U2, U3 and U4, all of which are characteristic of the Black Sea region and the Pontic-Caspian steppes.

The paucity of T is especially telling. Almost every European population has approximately 10% of hg T. The three exceptions are the Finns (4%), the Bosniaks (4%), and the Basques (1%). The Finns and Bosniaks have the lowest percentage of R1b in Europe, both under 5%. That the Basques, who have the highest frequency of R1b in Europe, should have the lowest incidence of mtDNA T is surprising to say the least. Unless, as I have theorised a few years ago, the Basques were conquered by a group of R1b men, who killed most of the local men and procreated with their women. This would lead to a society where the vast majority of the male lineages are foreign (R1b) but almost all the maternal lineages remain indigenous. That also explains why the Basque kept their pre-IE language, as children are more likely to learn their mother tongue, well from their mothers...

I have also revised the Basques' Y-DNA frequencies using four different sources (Underhill et al., Adams et al., Iberianroots and the study in link above) totalling 597 samples. There are only a few changes, but important ones. I2a decreased from 9% to 5% to the profit of E1b1b (increase from 1% to 2.5%) and G2a, which had 0% and now has 1.5%. We now have a pre-IE admixture suggesting a considerable West Asian admixture, since the total of G2a, J1 and J2 is 4.5%, about the same as the Paleolithic I2a1 (5%). The big question mark is E1b1b (2.5%), which would be Paleolithic as well as Neolithic, or even an influence of neighbouring Cantabria.

There are a few more oddities among the Basques. Two studies for traces of haplogroup Q (3 samples in total, so 0.5%). Iberianroots listed an individual who belonged to hg H, while the study in link above has one hg L (I double-checked the STR values, and the haplogroup assignment is correct). H + L ? How did those South Asian haplogroups end up there ? Did Q come along through the same migration from the Levant (Phoenicians, Neolithic farmers) ?