Hershey and chase experiment to prove that DNA is genetic material.

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Hershey (Alfred Hershey) and Chase (Martha Chase) performed a series of experiments in 1953 to prove that the DNA is the genetic material. The DNA was known to biologists since 1869, but still some scientists assumed that protein has some role in the inheritance. The key concept of their experiments was that Phage infection proved that DNA is the genetic material of viruses. When the DNA and protein components of bacteriophages were labelled with different radioactive isotopes, only the DNA is transmitted to the progeny phages produced by infecting bacteria.

First they labelled the bacteriophages with ³⁵S, since Sulphur is a component of protein coat of bacteriophage, the ³⁵S is incorporated to the coat of the bacteriophage. This bacteriophage was allowed to infect the bacteria. The bacteriophages infect the bacteria in a manner that their protein coat is left behind out side the bacterial cell and only the DNA of the bacteriophage enters the bacteria and incorporates with the genome of the bacteria. After the infection of the bacteriophage centrifugation is done to separate the capsids and the bacterial cells. It was found that ³⁵S was only found in the protein coat and not in the bacterial cells.

Secondly they labelled the bacteriophages with ³²P. Since Phosphorus is the essential component of the DNA. The ³²P was incorporated in the DNA of the bacteriophages. These labelled bacteriophages were allowed to infect the bacteria. The bacteriophages left their protein coat outside the bacterial cell and they injected their DNA into the bacterial cell which incorporated with the genome of bacteria. Then centrifugation was done to separate the protein coat and the bacteria. On testing ³²P was found in the bacterial cell. And not in the protein coat.

This experiment prominently proved that the DNA is the only genetic material, and the protein has nothing to do with the inheritance and genetic information.