I have an Italian last name and we know my great-grandparents immigrated from Italy as children and met and married in the United States.
That would make my grandfather 100% Italian ancestry and my dad 50% (grandma was Scandinavian).
I came in at 5.6% Italian rather than the 25% I expected. I don't know if that reflects migration into Italy in the past, grandma/great-grandma messing around, not getting equal percentages of DNA from each line, or what.