Final answer:
In the Hershey and Chase experiment, the radioactive isotope 32P was used to label DNA, supporting the conclusion that DNA is the genetic material.
Step-by-step explanation:
In Hershey and Chase's experiment to show that DNA is the genetic material, the radioactive phosphorus isotope 32P was used to label DNA. Hershey and Chase used radioactive isotopes to distinctly label the nucleic acids and proteins of the T2 bacteriophage. They chose 32P because phosphorus is a component of DNA and not protein, which ensured that only the DNA would be radiolabeled, and not the protein casing. As a result, when bacteria were infected with phages labeled with 32P, only the DNA entered the bacterial cells, providing strong evidence that DNA, and not protein, carries the genetic information.