Final answer:
If DNA replicated conservatively, after two generations, there would be one old, heavy band and one new, light band, but the Meselson-Stahl experiment showed a hybrid and a light band, supporting semiconservative replication.
Step-by-step explanation:
In the Meselson-Stahl experiment, if DNA were replicated conservatively, after two generations of replication there would be two types of bands: one old, heavy band and one new, light band. This outcome would imply that in each replication event, the original DNA molecule is conserved and a completely new molecule is synthesized. However, their experiment observed one hybrid band (of intermediate density) and one new, light band after two generations, which supported the semiconservative model of DNA replication, ruling out the conservative (and dispersive) models.