My family have long suspected that my paternal grandfather was not the biological son of his known father. I have considered having my dad take a Y-DNA (he is willing to do so) but am I correct in assuming that this would only be able to tell us whether my grandfather was the biological son of his father or not if other descendants of his paternal lineage have also taken the the Y-DNA test and are willing to compare results to see if they match or not? Because so far, I have not found any other descendants of this paternal lineage online and there is no surname project for our family name that I can find either. Until I can find someone with the same paternal lineage, would taking a Y-DNA test be a waste of time and money if my main intent is to find out whether my grandfather was biologically related to his father or not?