Males inherit their Y-chromosome from their fathers. The analysis of my brother’s Y-chromosome (which would be the same as my father John SIM, grandfather George SIM, great grandfather John William SIM, 2xgreat grandfather James SIM, -any male in our family with the SIM surname) shows that it belongs to the R-U152 group. This branch is called the Italo-Celtic branch which probably originated in the Alpine regions of Southern Europe during the Bronze and Iron Ages. It is found throughout most of Western Europe, but highest concentration today is found in Northern Italy near the Alps.
The word Celtic in the name of this branch is not in reference to what we normally think of as the Celts of the U.K. Celtic here means the Indo-European people during the Iron and Bronze Ages that had a distinct set of languages and cultures.
Read more about the Celts: https://en.wikipedia.org/wiki/Celts and https://www.ancient.eu/celt/
Between 500 and 100 B.C., waves of these warring tribes came to Britain directly from Europe or by way of the Iberian Peninsula. The SIM ancestors eventually made their way to Scotland.