Unequivocal proof that DNA is the genetic material was first proposed by 

The Hershey-Chase experiment, conducted in 1952, provided unequivocal proof that DNA is the genetic material but not protein. They conducted transduction experiments with T2 bacteriophage, a type of virus that infects bacteria (Escherichia coli). They radioactively labeled the viral DNA with phosphorus-32 (³²P) and the protein coat with sulphur-35 (³⁵S). After the viral infection cycle, they observed that only the labeled DNA entered the bacterial cells and played a role in the production of new viruses.