Haplogroup I2a1 M423 > L621 > CTS10228 (Slavic-Carpathian)

According to genetic research by Poreklo.rs, based on a large sample of over 2,000 ethnic Serbs, the Y-DNA haplogroup I2a1 M423>L621>CTS10228, known as the Slavic-Carpathian branch, represents the single largest paternal lineage among Serbs. It accounts for approximately 38% of Serbian paternal lineages and is uniformly distributed across Serbia and other ex-Yugoslav countries with no region below 30%.

This branch is estimated to be no older than 500 BC, making it a relatively young but dominant marker strongly associated with Slavic populations in the Balkans. It significantly outnumbers other haplogroups in the Serbian gene pool.

Sources

https://www.poreklo.rs/2019/06/12/y-dna-haplogroups-of-ethnic-serbs/