A.D. Hershey (born Dec. 4, 1908, Owosso, Mich., U.S.—died May 22, 1997, Syosset, N.Y.) was an American biologist who, along withMax Delbrück andSalvador Luria, won theNobel Prize for Physiology or Medicine in 1969. The prize was given for researchdone onbacteriophages (viruses that infect bacteria).

Hershey earned a doctorate in chemistry from Michigan State College (now Michigan State University) in 1934 and then took a position at Washington University School of Medicine in St. Louis, Mo. He joined the staff of the Genetics Research Unit of the Carnegie Institution of Washington in 1950 after giving up his position as professor at Washington University. In 1963 he became director of the Genetics Research Unit.

Hershey, Delbrück, and Luria began exchanging information onphage research in the early 1940s. In 1945 Hershey and Luria, working independently, demonstrated the occurrence ofspontaneous mutation in both the bacteriophages and the host. The next year, Hershey and Delbrück independently discovered the occurrence of genetic recombination in phages—i.e., that different strains of phages inhabiting the same bacterial cell can exchange or combine genetic material. Delbrück incorrectly interpreted his results as specifically induced mutations, but Hershey and one of his students proved that the results they had obtained were recombinations by showing that the genetic processes in question correspond with the crossing-over of parts of similar chromosomes observed in cells of higher organisms.

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Hershey is most noted for the so-called blender experiment that he performed withMartha Chase in 1952. By showing that phageDNA is the principal component entering the host cell during infection, Hershey proved that DNA, rather than protein, is the genetic material of the phage.