My great-grandmother's family, the Tsakgalou's, were living in Constantinople during the Greek/Armenian Genocide. While conducting research into my genealogy over the last 10 years, I've heard the Greeks from that region referred to as being Anatolian and Pontic. Is there a difference between the two terms? Would Greeks from Constantinople have belonged to one or the other?
For what its worth, I had my grandmother (who just turned 90 btw) take a DNA test a few years ago. She came out as being 75% Greek, 12% Eastern European, 6% Caucasus, 3% Middle Eastern, 1% Western European, and 1% European Jewish.
The main difference is mostly local cultural differences in tradition and language. The Pontic Greeks lived in regions that were once defined as Pontus, which was the north eastern Anatolian coast facing the Black Sea. Some Pontic Greeks also lived in Russia/Soviet Union, similarly in the coastal areas of the Black Sea. Greeks living in other parts of Anatolia were mainly just called Greeks, but different areas had some differences in dialects. Also the Karamanlides people was counted as Anatolian Greeks under the population exchange 1923, even though they spoke Turkish as their primary language. There were also Cappadocian Greek who lived in central Anatolia, they to were expelled to Greece. There probably were other smaller groups to that I don't know about. Some Greeks from these groups choose to convert to Islam and claimed Turkish identity so that they could stay.
Most of the Anatolian Greeks also spoke Turkish as a second language or first language. Some of the areas they were expelled to in Greece, they actually were discriminated against for being to much turkified. Similar things happened to Turks expelled from Greece, as most of did not even speak Turkish, they were not seen natives but outsiders.
All these Greeks are today referred to as Anatolian Greeks, and the Greek population of Istanbul are sometimes also referred to as Anatolian or Ottoman Greeks. In fact there was no further classifications of the Ottoman millet of Rum, which referred to all Greek Orthodox subjects of the Ottoman Empire. To summarize quickly, the main difference would probably be some cultural, traditional and language differences between the different groups of Anatolian Greeks. But those Pontic Greeks that lived outside Anatolia did not count as Anatolian Greeks, and are referred to as Pontic Greeks from the Soviet Union. These differences from mainland Greece and different perspectives on Hellenism caused some problems in the early years after the population exchange, but the Anatolian Greeks are mostly integrated in modern Greek society today.
Sources:
Bryer, Anthony. "The Pontic Greeks before the diaspora." Journal of Refugee Studies 4.4 (1991): 315-334.
Clogg, Richard, and Richard Clogg. A short history of modern Greece. Cambridge: Cambridge University Press, 1979.
Clogg, Richard. "A millet within a millet: the Karamanlides." Ottoman Greeks in the Age of Nationalism: Politics, Economy and Society in the Nineteenth Century (1999): 115-42.
Fann, Patricia. "The Pontic Myth of Homeland: Cultural Expressions of Nationalism and Ethnicism in Pontos and Greece, 1870–1990." Journal of Refugee Studies 4.4 (1991): 340-356.
Giannuli, Dimitra. "Greeks or" Strangers at Home": The Experiences of Ottoman Greek Refugees during Their Exodus to Greece, 1922–1923." Journal of Modern Greek Studies 13.2 (1995): 271-287.
Gondicas, Dimitri, and Charles Issawi. "Ottoman Greeks in the Age of Nationalism." (1999).
Mackridge, Peter. "Greek-speaking Moslems of north-east Turkey: prolegomena to a study of the Ophitic sub-dialect of Pontic." Byzantine and Modern Greek Studies 11 (1987): 115-137.
Motti-Stefanidi, Frosso, and Jens B. Asendorpf. "Perceived discrimination of immigrant adolescents in Greece." European Psychologist (2012).