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I2-L621 (Dinaric)
I2a1b1, commonly known as the Dinaric branch (I2-L621/PH908), is one of the most widespread paternal lineages of southeastern Europe. Emerging during the late Iron Age, it experienced explosive demographic growth associated with the proto–Slavic expansion during the early medieval period. This branch is central to the paternal ancestry of many South Slavic populations and is among the most frequently discussed European Y-DNA lineages in genetic genealogy.
The highest frequencies occur in the western Balkans, particularly Bosnia and Herzegovina, Serbia, Croatia, Montenegro and parts of Slovenia. Elevated levels also appear across Ukraine, Poland, Slovakia and Belarus, reflecting historical Slavic migrations. Minor frequencies appear in Germany, Austria, Romania and Greece.
I2a1b1 forms the largest and fastest-expanding branch of I2a1b. Downstream diversification into PH908, CTS10228 and related clusters corresponds to the period of Slavic ethnogenesis. Internal topology includes major parallel radiations distinguishable by region-specific distributions across Balkan and East-Central European populations.
I2a1b1's prominence in southeastern Europe makes it one of the most studied European Y-haplogroups. Its demographic signature mirrors the Slavic expansions and subsequent medieval population dynamics in the Balkans.