- Alfred Hershey and Martha Chase (1952) gave proof that DNA is the genetic material.
- In the experiment, bacteriophages (viruses that infect bacteria) were used.
- They grew some bacteriophages on a medium that contained radioactive phosphorus and some others on a sulphur-containing radioactive medium.
- The bacteriophages grown in the presence of radioactive phosphorus contained radioactive DNA. Radioactivity was not observed in the protein part. This is because DNA contains phosphorus but protein is devoid of phosphorus. In the same way, bacteriophages grown on radioactive sulphur contained radioactive protein, but not radioactive DNA. This is because DNA does not contain sulphur.
- Radioactive phages were allowed to attach to E. coli bacteria. As the infection proceeded, phage coats were removed from the bacteria by centrifuging. The phage particles were separated from the bacteria by rotating them in a centrifuge.
- Bacteria which were infected with phages that had radioactive DNA were radioactive, indicating that DNA was the material that passed from the phage to the bacteria.
- Bacteria that were infected with phages that had radioactive proteins were not radioactive. This indicated that the proteins did not enter the bacteria from phages. It proved that DNA is the genetic material that is passed from the bacteriophages to the bacteria.