I have a match between my uncle and another man who was born 2 years prior to my uncle and put up for adoption. I believe they are half brothers, sharing the same father. They match on all markers except one: DYS 456 17 (my uncle) DYS 456 16 (possible half bro). Does this one number difference on one marker mean that they can't be brothers? Do they share grandfathers instead?

I'm attaching the comparison chart of the two DNA tests.

Thanks!