Alfred Hershey and Martha Chase conducted an experiment in 1952 to determine whether DNA or protein serves as the genetic material. They worked with bacteriophages, viruses that infect bacteria, to study how genetic information is transmitted. In their experiment, they grew bacteriophages in two different radioactive media—one containing radioactive phosphorus (³²P) to label DNA, and the other containing radioactive sulfur (³⁵S) to label proteins. Since DNA contains phosphorus but not sulfur, and proteins contain sulfur but not phosphorus, this allowed them to track which molecule entered the bacterial cell during infection.

When the radioactive bacteriophages infected E. coli bacteria, the researchers observed that only the ³²P-labeled DNA entered the bacterial cells, whereas the ³⁵S-labeled proteins remained outside. After using a blender to separate the viral coats from the bacterial cells and then centrifuging the mixture, they found that the bacteria infected with ³²P-labeled DNA showed radioactivity, proving that DNA had been transferred into the bacterial cells. On the other hand, bacteria infected with ³⁵S-labeled proteins did not show any radioactivity, confirming that proteins did not enter the bacterial cells.

From these results, Hershey and Chase concluded that DNA, and not protein, is the genetic material, as it was responsible for directing the formation of new viruses inside the bacterial cell. Their experiment provided strong evidence supporting the role of DNA in inheritance, laying the foundation for modern molecular genetics.