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I recently tested my dad's Y DNA at the 37 marker level. He has one match with a genetic distance of 1. This person shares our surname. The other match has a genetic distance of 4 and doesn't share our surname.

Would it be advantageous to update to Y-67?

Although we have a common surname, we don't know which state his earliest ancestor is from and who his parents were. His closest matches on Family Finder don't have the same surname (from a 23andme data transfer).

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In Y-DNA STR tests like this, the main advantage of having more markers tested (e.g. 67 versus 37) is being able to tell which matches are the closer ones and which ones are more distant when you have lots of matches at the same or almost same genetic distance. As more markers are compared, the more distant matches among them are more likely to show additional marker mismatches than the closer matches are.

Another possible advantage is having a slightly better idea of how close a match is when considered alone. However, this closeness can't be characterized at all precisely. For instance, your father's same-surname, one-mismatch in 37 relative is loosely characterized by FTDNA as "Tightly Related". With a 67 marker test, this same person would probably have a total of between 1 (we know he has at least one) and 5 marker mismatches and would fall into one of three groups according to FTDNA, the closest termed "Tightly Related" and the other two termed "Related".

Additional marker resolution will not turn up other "Tightly Related" matches. It might find some matches that have more than 4 mismatches at the 37-marker level but not many additional mismatches at the 67-marker level. If it does, those matches would only fall into the more distant FTDNA categories: "Related", "Probably Related", or "Only Possibly Related".

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