62584d79_me_STR_markers_be_interpreted___Relationship
[Genetic Distance] 0 [Interpretation] A perfect 12/12 match between two men who share a common surname (or variant) means they likely share a common male ancestor within the genealogical time frame. The combination of these facts demonstrates their relatedness.However, if the surname is one of the most common (trades or towns), i.e., Smith, Tailor, Miller, etc., then we suggest you utilize additional markers to eliminate the possibility of a coincidental surname and genetic match. [Relationship] 
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FTDNA Learning Center – If two men share a surname, how should the genetic distance at 12 Y-chromosome STR markers be interpreted?
Relationship