” ‘No one who has invested a mere month of effort in researching his family tree would be surprised by the DNA test findings.’ -— For most people, yes. A small percentage, like me, would discover that 25% of his tree was wrong, due to rape.”
Non-paternity events (NPEs) include any event which has caused a break in the link between an hereditary surname and the Y-chromosome resulting in a son using a different surname from that of his biological father.
NPEs are very common, maybe one in every 5 to 25 births, depending on culture. NPEs include name changes, adoptions, rape, affairs, and sperm donors.
To discover the true paternal line, a male should take a Y-DNA test at Family Tree DNA.
FamilyTreeDNA has the most precise Y-DNA haplogroups (different prices for different levels of precision) but that is in addition to the basic “autosomal” test. 23andMe has Y-DNA haplogroups as part of the basic test (obviously for men only)—not as specific but may be adequate to compare one man’s haplogroup with that of a known descendant of the putative father.