Ottoman invasion caused migrations and many Serbs from valleys and plains moved to mountains, migrated on Austrian and Venetians territories or converted to islam and stayed in the valleys/plains. In the mountains Serbs were pretty isolated from Ottomans, unlike in valleys/plains. When the Ottomans collapsed many Serbs came down from the mountains to plains and valleys from were their ancestors once escaped. For example Serbs from fertile basin Župa (
http://vinozupa.com/en/company/history-of-zupa/) in central Serbia mostly came from nearby mountain Kopaonik (
https://en.wikipedia.org/wiki/Kopaonik) in 19th century when Ottomans left that area. There was a research of y dna of Serbs from Župa area in 2014; I2a-Din is about Serbian average, R1a is higher than Serbian average, E-V13 is sbout average etc. Александровац етнички Срби 85 Тодоровић (2014)
https://sr.wikipedia.org/wiki/Генетс...је
Александровац is the center of Župa.