In one part of their experiment, Hershey and Chase used radioactive phosphorus to label the DNA of their T2 bacteriophages. What conclusion did they arrive at as a result? A. They found radioactive phosphorus in the bacteria, indicating that DNA was the genetic material. B. Radioactive phosphorus did not transfer into the bacteria, prompting them to continue their investigations with radioactive sulfur.

Correct Answer is A. They found radioactive phosphorus in the bacteria, indicating that DNA was the genetic material.

Hershey and Chase were investigating which component of the T2 bacteriophage - DNA or proteins - was the genetic material that was injected into bacteria and responsible for the production of new viruses. In their experiments, they used radioactive phosphorus, which can be incorporated into DNA but not into protein. After allowing the radioactively labeled phages to infect E. coli bacteria, Hershey and Chase found that the radioactive phosphorus was indeed inside the bacterial cells. This meant that the DNA, not the protein, of the virus had entered the cells. This supported the conclusion that DNA was the molecule carrying genetic information.

Extra: The significance of the Hershey-Chase experiments lies in the debate at the time over whether proteins or DNA was the hereditary material. While proteins were considered good candidates due to their complexity and diversity, DNA was comparatively simple, made up of only four types of nucleotides. By cleverly labeling DNA and proteins with radioactive isotopes (phosphorus-32 for DNA and sulfur-35 for proteins), they were able to track which of these molecules entered the bacterial cells during phage infection. Since they found that only the radioactive phosphorus (from DNA) entered the bacteria, this provided strong evidence that genes are made of DNA. This was a pivotal moment in molecular biology, setting the stage for the discovery of the structure of DNA and the understanding of how genetic information is stored and transmitted.