The most accepted theory is that Serbs are one of the Slavic tribes who arrived arrived in Balcans during the Early Middle Age. When they arrived here they found some people here, the Illyrians, the ancestors of the Albanians and it's obvious that there was some mixture between the natives and the newcomers. And from that moment until in our days there are 1500 years of history and during all these centuries both people lived side by side. Just if you have a look at the surnames of the today Serbs you will find plenty of Albanian surnames, always ending with the Slavic suffix iç. Without going deeper, you can find Serbs with surname Gegiç and Toskiç, let alone other surnames. For the God sake, we have to decide if the surname of the President of Kosova Thaçi was Thaçiç or the surname of the Foreign Minister of Serbia Daçiç was Daçi. Knowing the history and how the assimilation works in my humble opinion the surname Daçi turned in Daçiç. This suggests that there is some Albanian contribution on the genetic of the modern Serbs.