I've also heard some Italians say that there are even slight genetic differences not only between Northern and Southern Italians, but even between Calabrians, Sicilians, Neapolitans or Apulians. Apulians for one have a large amount of Illyrian blood ( related to Albanians and modern Northern Greeks), Calabrians are said to have substantial old Greek ancestry (related to Mani Greeks and Cretans) and also Jewish ancestry, Sicilians are a mix of different elements such as native Sicili tribes, Greeks, Normans, Arabs, Berbers and Spanish, Neapolitans seem to have the biggest amount of Italic ancestry with some Spanish. I'm not an expert on genetics, but it's clear that not many other European people seem to divide themselves between regional lines as the Italians do. In the region I live are a lot of people of 'Italian' descent. Rarely do they describe themselves as 'Italian'. In most cases they see themselves as Calabrese or as Sicilian (there aren't many Neapolitans or Apulians over here).

That attitude is also evident with some other groups of people. Albanians for instance seem to divide themselves on a linguistic as well as genetic base between Kosovars, Northern Albanians (Ghegs) and Southern Albanians (Tosks).
Corsicans in France would never (and I do mean NEVER) describe themselves as 'French'.
Regional differences exist in England: people in Merseyside and in turn in the whole Northwest of England describe themselves as 'Scousers' and take pride in being a mix of Anglo-Saxon, Irish, Welsh, Scandinavian and even African elements.
Formerly only people from the East End of London described themselves as 'Cockney' but the 'Cockney-heritage' also spread to the South of London and areas surroundin Greater London. 'Cockneys' seem to come from a mix of Anglo-Saxons, Irish, French (Huguenot), Jews and Romanis who settled in the 18th century industrial area of the East End. Cockney families spread to the South of London, Essex, Kent,...and other nearby areas.
In Greece the regional Macedonian Greeks, Maniots and Cretans also claim to have different ancestries.

What all of these people do have in common however, is the family-oriented structure.