 Although genes were known to exist on chromosomes , chromosomes are composed of both protein and DNA , and scientists did not know which of the two is responsible for inheritance . In 1928 , Frederick Griffith discovered the phenomenon of transformation ( see Griffith 's experiment ) : dead bacteria could transfer genetic material to " transform " other still @-@ living bacteria . Sixteen years later , in 1944 , the Avery – MacLeod – McCarty experiment identified DNA as the molecule responsible for transformation . The role of the nucleus as the repository of genetic information in eukaryotes had been established by <unk> in 1943 in his work on the single celled alga <unk> . The Hershey – Chase experiment in 1952 confirmed that DNA ( rather than protein ) is the genetic material of the viruses that infect bacteria , providing further evidence that DNA is the molecule responsible for inheritance . 
