Alfred Day Hershey (1908-1997), the American biologist. In 1952, with Martha Chase, Hershey proved that DNA (deoxyribonucleic acid) carries genetic information. They labelled the DNA and protein coats of bacteriophages, viruses that infect bacteria, with different radioactive markers. The viruses injected their DNA into the bacteria, leaving their protein coats outside. The injected DNA then hijacked the bacteria's genetic machinery to make new bacteriophages, complete with protein coats. Hershey won the Nobel Prize for physiology or medicine in 1969.