Final answer:
Meselson and Stahl used E. coli and different Nitrogen isotopes to investigate DNA replication. They found evidence supporting the semiconservative replication model.
Step-by-step explanation:
Meselson and Stahl used E. coli and different Nitrogen isotopes to investigate how DNA replicates. They grew E. coli in a medium containing a 'heavy' isotope of nitrogen (¹5N), which becomes incorporated into DNA. After one round of replication in a medium containing ¹4N, the DNA was isolated and separated by ultracentrifugation.
The results showed that the DNA formed a band at an intermediate position between the bands of DNA grown exclusively in ¹5N or ¹4N, suggesting semiconservative replication.