The populating of Europe was significantly influenced by the Ice Age.
Since the cold weather conditions were not conducive to roaming around, people who included the Eurasian maternal lines (yellow lines in the map above) secluded themselves in refuges (see map below) around the north of Spain, France, Italy and the Balkans.
The primary European mt-haplogroups are H, J, K, T, V and U (all derived from the macrohaplogroup R). X is included in Sykes’ seven European maternal lines but is also found in Asia and the Americas. Other mt-DNA haplogroups found in Eurasia, derived from the N macrohaplogroup, are I and W.
Once the ice melted it seems there was a frenzy of migration from east to west and south to north, and vice versa. People of European geographic ancestry share pretty much the same maternal Haplogroups with two, Helena and Ursula, dominating a vast area of Eurasia.
Mt-haplogroup H (Helena) is most common in Europe and the most common haplogroup in the Near East. Other haplogroups are also common in Europe and the Middle East and not found elsewhere.
European paternal lines came from three directions. The earliest migrants came from the Middle-East. Later migrants came from the Central Asian steppes and soon after, the North East European paternal line came across from North Asia. Whether the earlier paternal lines were also holed up in refugees for a while is not certain.
The first paternal line to arrive in South Europe, at least as far as the Mediterranean, was E. E is still widespread in relatively small proportions across Europe predominantly due to much later migrations. Y-Haplogroup E is fully explained elsewhere, and was part of all early Mediterranean civilisations.
The next European paternal line was I, coming up from the Middle-East via the Balkans and then moving north to Scandinavia, and perhaps also taking a sea route across the Mediterranean before settling in Sardinia where it is prevalent today.
From Genebase: Likely origin of haplogroup I from the Middle East via the Levantine corridor and its residence in two pockets (gray ovals) during the last glacial maximum in Europe. Subclades of haplogroup I are color coded and corresponding SNPs listed in the legend. The routes and locations are based on evidence from several studies of Y-DNA I haplogroups and haplotypes.
Haplogroup I2 may have originated in South East Europe about 17,000 years ago and split into four subgroups: I2a1, I2a2, I2b1 and I2b2.
In the far north of Europe, the I1a (M253) paternal line is found amongst the Saami
of north Finland. Whilst, 90% of maternal lines in Saami women are descended from U5 or V.
The ancestors of these maternal and paternal lines very likely over-wintered in or close to Iberia during the Last Ice Age before migrating further northwards.
It seems clear that the paternal line from the Central Asian steppe, R1, arrived some time after the ice had receded.
About half of Europeans in the UK, Spain, France and wider afield are descended from Helena and half of the men are descended from R1b (and some men from both H maternal and R1b paternal lines). The original carriers of mtDNA H1 came from Iberia (Ottoni et al, 2010).
Ireland has an unusually high incidence of R1b (80+%). Maciamo on Eupedia suggested that the myth of the leprechaun may date back to a time when tall Bronze Age migrants came in search of precious metals to smelt – because leprechauns are little people who hide precious metal! Perhaps that is a fanciful idea, yet the history of South America and Africa show what lengths people will go to to find the necessary ores for industry.
The frequencies of H maternal and R1b paternal lines reach their highest in the Royal Houses of Europe, over 95+%!
North Europe was populated from the same sources and the East/West cline from the UK to Russia has a value of only 0.0032.
Southern Europe has more admixture from the Middle East and North Africa.
Italy was blocked off by the Alps and Italian data creates a large North/South cline.