DNA replication — The Meselson–Stahl experiment demonstrated which model of DNA replication?

Introduction:
The Meselson–Stahl experiment (E. coli grown in heavy nitrogen followed by a light nitrogen shift) is a landmark demonstration of how DNA duplicates during the cell cycle. The question asks which replication model their data supported.

Given Data / Assumptions:

• Three proposed models existed: conservative, semiconservative, dispersive.
• Density-gradient centrifugation can separate DNA by buoyant density (heavy vs light).
• Parental strands serve as templates during replication.

Concept / Approach:
Semiconservative replication predicts that each daughter DNA molecule contains one parental (heavy) strand and one newly synthesized (light) strand after one generation in light nitrogen, yielding hybrid density DNA.

Step-by-Step Solution:

Verification / Alternative check:
Conservative replication would show distinct heavy and light bands after one generation; dispersive would maintain only intermediates without a pure light band even after several generations.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing labeling (heavy vs light) with strand composition; forgetting the generational pattern of bands.

Final Answer:
Semiconservative replication.