Modern Balkan populations descend from:
- Iron Age Balkaners
- Roman-era Western Anatolians
- Early Medieval Slavs
- Ottoman-era Western Anatolians

Their Slavic and Anatolian ancestry is inversely correlated.

Early Slavs had ~70% Baltic-related ancestry and ~30% Balkan-related ancestry (possibly Dacian, source population currently unknown).

Roman-era Anatolians were genetically ~40% Mycenaean Greek and ~60% Indo-European Anatolian (Hittie, Luwian, etc.).

Ottoman-era Anatolians descended directly from the Roman-era population, but had variable levels of Turkic ancestry.

The Oghuz Turks who conquered the Byzantine Empire were approximately half Scythian, half Mongolian/Siberian.

Admixture analysis source:
A genetic history of the Balkans from Roman frontier to Slavic migrations (2023)