Can a DNA test proove that I am a cohen?

Demonstrating that one has the “Cohen gene” does not prove that someone is a Cohen, since numerous non-genetic factors may disqualify someone from being a Cohen. If the families were fully Halachically observant, and have a family tradition that they were Cohanim, one can assume that one is a Cohen. This means, that the observant antecedents received the first Aliyah to the Torah or performed Nesiat Kapayim (duchening). If not, one should not assume that one is.