There’s a theory about Slavs migrating out western Ukraine by scholars. Schools students and undergraduate students are presented with this theory in Slavic countries. Maybe those propopents are are right, as that region to which they point has good climate with fertile soil able to sustain a large population that settled central & eastern Europe, and the Balkans.
The Belarusian guy Vadim Verenich , who maintains the MDLP project, has done a lot of work on the so-called Slavic (Dinaric) branch of I2a marked by I2a-CTS10228. The mutation of the marker is around 2,200 years of age. Both Vadim Verenich and Ken Nordtvedt mantain I2a-CTS10228 marker originated outside of the Balkans in north Carpathians, because the marker has greater diversity in that region. Vadim Verenich has I2a-CTS10228 marker himself. His ancestry is from Polessia , southern Belarus.
Update tree (October, 2016) I2 with the branch marked by I2a-CTS10228 commonly found in Slavic countries.