In human genetics, Haplogroup R1a1 (M17) is a Y-chromosome haplogroup that is spread across Eurasia.
It is common in Europe, Central Asia, and South Asia. In Europe, the highest frequencies are found in Central and Eastern Europe. Today it is found with its highest levels in Hungary (60%, 20%), Poland (56%), Ukraine (54% or 44%), and Russia, where one out of two men has this haplogroup.
Relatively high frequencies are also found in Northern Europe, the largest being 23% in Iceland, and it is believed to have been spread across Europe by the Indo-Europeans or perhaps later migrations of Vikings, which accounts for the existence of it in, among other places, the British Isles.
Lower frequencies of R1a1 are found among populations of West Asia.