Quote Originally Posted by Aberdeen View Post
I guess that's the only explanation that makes sense to me. Although J2 in Greece as a whole is only 19%, I notice that it's 34% in Crete, which probably has a population that's closer to the DNA profile of pre migration period Greece than modern mainland Greece is. So, if Greece used to be higher in J2, all that colonization of the Italian peninsula for centuries would have resulted in a lot of J2 in Italy, and particularly in the most Greek colonized parts of Italy. But, as you suggested, the muslim invasions of southern Italy would have somewhat decreased the J2 in some of those areas of southern Italy that were previously heavily colonized by Greeks, reducing the J2 level in those areas as compared to other heavily Greek colonized parts of Italy. I guess it all fits.
What muslim invasions are you talking about? Muslims barely left any Y-DNA beyond few spots here and there. Anyway most of J2 in Italy is non Greek. The dominant J2 subclade in Greece is almost completely absent in Italy, excluding for areas which were colonized by Greeks and Albanians (Eastern Sicily, Salento, Southern Calabria).