The significance of a YDNA genetic distance of 1 depends, in part, on how many STRs were tested. If there was a GD of 1 between 2 111-STR marker tests, that suggests a possible close relationship. A GD of 1 between 2 12-STR marker rests is pretty meaningless. No YDNA test, however, will prove a father-son relationship. For that, you need an autosomal DNA test like 23 and Me or Family Tree DNA's Family Finder test. An autosomal DNA test should show that a parent and child share about 50% of their DNA. If they share close to 50% then it is virtually certain they are either parent-child or siblings.