Since the idea that I2a-CTS10228>Y3120 might not be Slavic keeps coming back, I am posting a summary of what the current data tells about it's origins and arrival to the Balkans.
Ancient DNA:
1- The earliest I2a-CTS10228 found so far is a Polish 9th cent I-S17250. It's closest relative on the
YFull tree is from Ukraine.
2-
I2a is absent in a 5th-6th cent cemetery in Hungary. This was a Longobard cemetery in use during and after the Germanic migrations but before the Slavic ones. Small sample (21) but there were several Germanic lines, and even a few more southern ones, but no I2a.
Modern DNA:
1- SNP diversity
As can be seen on
YFull. Out of 5 major I-Y3120 branches:
-2 are only found in in Eastern Europe (Y3120* & Y4460) -tmrca 2200 for Y4460
-1 is most diverse in Greece, secondly in Eastern Europe (Y18331) - tmrca 2200
-1 is pretty even in diversity between Eastern Europe & the Balkans (I-S17250) - tmrca 1800
-1 is more diverse in the Balkans, secondly in Eastern E. with MRCA equal/close to the whole branch (I-Z17855) -tmrca 1600
So Eastern Europe currently has more branches, more diversity within them, and more distant MRCAs.
2- STR diversity
It has been calculated (
here, p.26) that haplotypes with:
- DYS448=19 (I2a-DinSouth) are most diverse in the Poland-Belarus area
- DYS448=20 (I2a-DinNorth) are most diverse in Ukraine
To summarize, current data suggest a huge expansion out of Eastern Europe which reached the Balkans no earlier than the 5-6th century CE.