My parents both came from fishing families in adjacent villages in the East Neuk of Fife, near St. Andrews. My father's ancestors were almost entirely from that area, with one exception who seems to have come from Perthshire, not very far away. So, pretty homogeneous, and as Fife was part of ancient Pictland or "Caledonia", I wasn't surprised to be told that my particular variety of YDNA R1b-L21 (common as muck in western Europe), was R1b-Pictish. From the evidence of place-names and personal names, the Picts seem to have spoken a form of Celtic close to Welsh. Their former territories have for example lots of Aber- names, whereas the western areas settled by Gaels from Ireland have Inver-.
My mother's family-tree is more diffuse, but even there, ancestors from Northumberland, the Scottish Borders and Northern Ireland don't explain all the fancy bits and pieces in my DNA ethnicity breakdown.
Harry