Greek genetic connections/IBD sharing to Western Europe: why and how?

[Hithaeglir]

If it's just for the Peloponnesus and France the most recent historical event that could explain this sharing is the Frankish rule of Peloponnese, but imo it wasn't that long to create such an impact on the peloponnesian genetics,most likely it's something that predates that.

In 1205, following the dissolution of the Byzantine Empire by the forces of the Fourth Crusade, the Crusaders under William of Champlitte and Geoffrey of Villehardouin marched south through mainland Greece and conquered the Peloponnese against sporadic local Greek resistance. The Franks then founded the Principality of Achaea, nominally a vassal of the Latin Empire, while the Venetians occupied a number of strategically important ports around the coast such as Navarino and Coron, which they retained into the 15th century.[24] The Franks popularized the name Morea for the peninsula, which first appears as the name of a small bishopric in Elis during the 10th century. Its etymology is disputed, but it is most commonly held to be derived from the mulberry tree (morea), whose leaves are similar in shape to the peninsula.[25]

Frankish supremacy in the peninsula however received a critical blow after the Battle of Pelagonia, when William II of Villehardouin was forced to cede the newly constructed fortress and palace at Mystras near ancient Sparta to a resurgent Byzantium. This Greek province (and later a semi-autonomous Despotate) staged a gradual reconquest, eventually conquering the Frankish principality by 1430.[26] The same period was also marked by the migration and settlement of the Arvanites to Central Greece and the Peloponnese.[27]

The Ottoman Turks began raiding the Peloponnese from c. 1358, but their raids intensified only after 1387, when the energetic Evrenos Bey took control. Exploiting the quarrels between Byzantines and Franks, he plundered across the peninsula and forced both the Byzantine despots and the remaining Frankish rulers to acknowledge Ottoman suzerainty and pay tribute. This situation lasted until the Ottoman defeat at the Battle of Ankara in 1402, after which Ottoman power was for a time checked.[28] Ottoman incursions into the Morea resumed under Turahan Bey after 1423. Despite the reconstruction of the Hexamilion wall at the Isthmus of Corinth, the Ottomans under Murad II breached it in 1446, forcing the Despots of the Morea to re-acknowledge Ottoman suzerainty, and again under Turahan in 1452 and 1456. Following the occupation of the Duchy of Athens in 1456, the Ottomans occupied a third of the Peloponnese in 1458, and Sultan Mehmed II extinguished the remnants of the Despotate in 1460. The last Byzantine stronghold, Salmeniko Castle, under its commander Graitzas Palaiologos, held out until July 1461.[28] Only the Venetian fortresses of Modon, Coron, Navarino, Monemvasia, Argos and Nauplion escaped Ottoman control.[28]

[Sikeliot]

I don't even know if 50 is really that high, that's why i wanted to see what's in the supplementary file. Russia two times higher than Polish or Ukraine, is a bit weird. It doesn't seem to be IBD btw just admixture, it says shared ancestry between K4 and K8 under the table. The IBD run is the heatmap of the regions all together.

For what it was worth, France was in the 40-50 range, and Spain in the 50-60 range. Italy in the 80-90 range.

[Percivalle]

The study on the Peloponnese that has been cited found that in addition to high IBD sharing with Italy, the next greatest is Spain, then France. IBD sharing to North Slavic people and Levantines was too low to be of significance. Other Balkanites were not surveyed for comparison.

IBD sharing to Andalusians ranged from 53.8% in Arcadia to 62% in Corinth, with other regions close to 60%. To France, they all hovered around 40%.

Why would Greeks have so much IBD sharing with SW Europe, based on history, migrations, and so on? Or is there a Celtic element in Greek genetics that often goes unmentioned?

It's not really IBD, it's shared ancestry, similar but not exactly the same thing. In the paper IBD sharing is only among Greeks.

[Sikeliot]

The point is though that shared ancestry with both Slavs and Levantines is low, but with French it approaches half. Why would this be?

[Percivalle]

The point is though that shared ancestry with both Slavs and Levantines is low, but with French it approaches half. Why would this be?

It's the goal of the paper.

[Sikeliot]

It's the goal of the paper.

But does it make sense?

Frankly I think if they measured sharing with Bulgarians it'd be much higher than for French or Spanish. I think they omitted other Balkan populations and it creates a misleading report.

Low IBD with the Levant and Russia makes sense.