Final answer:
Meselson and Stahl's experiment showed an intermediate density band after one generation, indicating semiconservative DNA replication with a mix of 15N and 14N.
Step-by-step explanation:
The experiment conducted by Matthew Meselson and Franklin Stahl provided significant insights into the mechanism of DNA replication. They utilized a heavy isotope of nitrogen (15N) to label the DNA of E. coli before shifting the bacteria to a medium containing a lighter isotope (14N). After one round of cell division in 14N, the DNA that was isolated produced a single band at a density between that of 15N and 14N, confirming the semiconservative replication model of DNA. This finding was evidenced by the intermediate band observed after one generation, which represented a mix of 15N and 14N. Had the DNA replicated conservatively, two separate bands would have been observed - one heavy and one light.