Today I heard somewhere, probably on Crashcourse History, something that was phrased very roughly as "Ottoman Turks are mostly descendants of people who already inhabited Anatolia before the Seljuk Turks arrived"
Even though I'm probably misremembering it somewhat, how true is this statement? And who were these people? I imagine mostly Greeks but Roman Empire was fairly multicultural.
hi! while you may get responses here, this question might do better in /r/AskScience (biology)
This question is sort of answered here:
A lot of Anatolia became Greek even before Alexander (550-350 B.C.) most of the coastal cities in Anatolia were Greek and that increased after the end of the Lydian empire. It stayed Greek through Rome/Byzantium. The Rus, Swedes and other slavs that settled over time eventually became Greek (culture, language etc). Later those Greeks became Turks and the vast majority of Turkey's population were native people in Anatolia who converted to Islam, rather than the actual Turkish tribes and other Islamic peoples who settled there.
The reason to convert to Islam is to not have to pay the Jizya (a tax only Non-Muslims called Dhimmi had to pay), they also converted to not be discriminated against or they converted to identify with the victor. Some may have also converted because they liked the culture and faith better than Christianity or Judaism.
As for genetics, I dont think you can find the answer you are looking for. From what I know the results are to broad. For example a result could show for someone that is Greek that they are Mediterranean rather than something very specific like Greek, descended from Mycenaeans etc.