Radioactive labels on a virus proved DNA, not protein, carries heredity
In 1952, Alfred Hershey and Martha Chase labeled a virus's protein coat with radioactive sulfur and its DNA with radioactive phosphorus, then let it infect bacteria. Only the phosphorus, meaning only the DNA, ended up inside the bacterial cells, while the protein shell stayed outside and could be washed away. The result settled a long-running debate by showing DNA, not protein, is the molecule that actually transmits genetic information.