In the hershey and chase experiment that confirm that dna, not protein, was the hereditary material, what was the key finding?

Radioactive phosphorus (32P) was present inside the host bacteria.

Explanation:

Hershey and Chase's experiment provided evidence that DNA carries genetic information. Alfred D. Hershey and Martha Chase (1952) used radioactive phosphorus (32P) and radioactive sulfur (35S). They infected the cells of the bacteria E. coli with the T2 bacterial virus (bacteriophage). They observed the presence of radioactive phosphorus-containing DNA of the viral particle inside the infected bacterial cells.

On the other hand, the sulfur-containing protein of the viral coat was not detected inside the infected bacterial cells. This proved that the viral DNA enters the host cell and carries genetic information for viral replication.