 Turning the clock back to the 1940s and 50s, the scientific community was in the midst of a debate about the nature of the hereditary material that is responsible for passing our traits onto our children, to our children's children, and so on for generations. Pretty existential question, right? An experiment by Avery McLeod and McCarty in 1944 first suggested that perteams were not responsible for heredity, as previously thought, and instead DNA was the culprit. However, given that their results flew in the face of the current thinking, not everyone was convinced. In science, a great deal of evidence is needed before a new scientific idea is accepted as fact. Therefore, in 1952, Alfred Hershey and Martha Chase carried out experiments which addressed a similar question. Was DNA the hereditary material or was it protein, or was it something else? To solve this important puzzle, Hershey and Chase needed a simple model organism to solve this complex question, and a clever experiment. They chose the simplest organism possible, a bacteriophage, which is a virus that infects bacteria. This virus looks a bit like a lunar landing module and attaches to the outside of the bacteria. It then injects a substance into the bacteria to create many new copies of the virus. These newly manufactured viruses are released when the bacteria bursts. So the substance injected inside of the bacteria must contain the instruction manual for making new virus. It contains the hereditary material. But what was this material that the virus injected into its host? The answer to their question might shed light on the nature of heredity for all life on earth. Viruses consist of two things, a DNA core surrounded by a protein coat. Hershey and Chase needed to figure out which of the two was injected into the bacteria. They ran two experiments and in each they labeled one of the components. For this labeling they used radioactive tags, radioactive sulfur for the protein, and radioactive phosphate for the DNA. This was an elegant method because phosphate is only found in DNA and not in the amino acids that make up proteins. And sulfur is only found in proteins and not DNA. After the viruses infected the bacteria, the researchers examined whether the radioactive signal was detected inside the bacteria or left outside. To do so they needed to separate the bacteria from the viruses attached to their outsides and did so using a warring blender, similar to that used for making milkshakes. Once separated they then centrifuge the sample since bacteria are bigger they were centrifuged to the bottom, while the smaller viruses remained at the top of the tube. When they prepared virus with sulfur labeled protein and mixed it with bacteria they found that most of the radioactivity remained with the virus and did not enter the bacteria. When they allowed the virus to replicate and collected the new viruses less than 1% of the protein radioactivity from the viral parents were found in the newly replicated virus so the protein was not being inherited. On the other hand when they performed the same experiment using virus with its DNA labeled with phosphate they found that most of the radioactive DNA was injected into the bacteria from the attacking virus and much of this labeled DNA was inherited and passed on to the new virus generation. Hershey and Chase added to the mounting evidence pointing the finger at DNA as the hereditary material but they were aware that their experiments left a few unanswered questions as experiments often do and they were cautious in their conclusions. From their observations they stated that DNA had some function in the multiplication of the virus whereas proteins did not. Word about the Hershey Chase experiment spread quickly and helped to convince many scientists that DNA indeed was the molecule of heredity and the remaining skeptics could not hold up for much longer. A year later Watson and Crick published their model of the DNA double helix which provided an elegant explanation for how DNA with such a simple structure could be replicated and pass along information from parents to offspring. The Hershey Chase experiment is considered a classic in biology because it tackled an important question with the use of a well-chosen model organism and an elegant experimental design in order to clearly distinguish between two competing hypotheses.