A maternal first cousin of my father had a DNA analysis.
The results were virtually 50% Italian and 50% WASP (my term). No reporting of North African, Arab, Greek, Norman, etc. which could be behind the Italian ancestry.
By paper trail his mother was 100% Italian (Sicilian) and his father was 100% WASP.
His mother was my paternal grandmother's sister. How confident can I be that this ancestry line - his mother and my paternal grandmother - have thoroughbred roots in Italy?
Also, since my paternal grandparents were third cousins to each other and their paternal lines converge five generations prior to them, can the results of my father's cousin be generalized to my paternal grandfather's line to any degree?
Moreover, if I had a DNA analysis and found any significant percentage of Sicilian precursors like North African, Arab, Greek, Norman, could I assume it came from my grandfather (introduced within five previous generations of him) rather than from my grandmother, given that my paternal side is 100% Italian by paper trail and my maternal side has none?
As a side-question, how much DNA would my father and his first cousin share, and how much would my father's first cousin share with me?
I realize that actual DNA analysis is the best path, but, in that absence, I wonder if any armchair inferences can be drawn?