Y chromosome haplogroup G is associated with the spread of Neolithic farmers from the Near East and Anatolia into Europe. It is found in modern populations at highest frequencies in the Caucasus region, in parts of the Middle East, and in isolated refugia populations in Europe — most notably in Sardinia. In most of continental Europe, G haplogroup men represent only a few percent of the paternal-line chromosomes, having been substantially diluted by the later Bronze Age steppe expansion that brought haplogroup R1b and R1a to dominance across much of Europe.
Finding Ötzi in haplogroup G2a2b is entirely consistent with his high Anatolian farmer ancestry. The farmers who expanded into Europe from Anatolia during the Neolithic primarily belonged to Y chromosome haplogroup G. As the steppe herders expanded across Europe in the Bronze Age, they brought their own Y chromosomes — haplogroup R1b in western Europe, R1a in eastern Europe — that dramatically reduced the frequency of G in most regions.
The persistence of G haplogroup in Sardinia reflects the same pattern seen in the whole-genome analysis: Sardinia, as an island relatively isolated from the continental Bronze Age migration, retained more Neolithic farmer genetics than most of mainland Europe, including higher proportions of G haplogroup men among modern Sardinians than in most other European populations.
The 19 modern Tyrolean men identified in 2013 as sharing a G2a2b mutation with Ötzi represent an unexpected trace of this haplogroup in a mainland European population that, based on overall population genetics, one might have expected to have been more completely replaced by steppe-associated chromosomes. Their survival in Tyrol may reflect exactly the Alpine isolation that the whole-genome analysis proposed for Ötzi’s community — a region where the mountains limited gene flow enough to allow an older Y chromosome lineage to persist.