Final answer:
Meselson and Stahl demonstrated that DNA replicates in a semiconservative manner. Their experiment involved growing E. coli in a heavy isotope of nitrogen, separating the DNA based on density, and observing that each DNA molecule consists of one old strand and one newly synthesized strand.
Step-by-step explanation:
Meselson and Stahl are best known for demonstrating that DNA replicates in a semiconservative manner. In their experiment, they grew E. coli for several generations in a medium containing a heavy isotope of nitrogen (¹5N), which incorporated into the DNA. By using centrifugation, they were able to separate the DNA based on its density and observed that after one generation of growth in ¹4N, the DNA formed a band at an intermediate position between ¹5N and ¹4N, indicating that each DNA molecule consists of one old strand and one newly synthesized strand. This experiment provided evidence for the semiconservative replication model of DNA.