Final answer:
Meselson and Stahl's experiments in 1958 demonstrated that DNA replication follows a semiconservative model, where each new DNA molecule contains one original and one new strand. Their findings rejected the conservative and dispersive models of DNA replication.
Step-by-step explanation:
Meselson and Stahl's experiments provided strong evidence for semiconservative replication of DNA. Their experimental design utilized isotopes of nitrogen to label the original DNA strands, allowing them to observe the patterns of inheritance of the labeled nucleotides following DNA replication. Their results showed that each new DNA molecule consisted of one old strand and one new strand, precisely as predicted by the semiconservative model. This was evidenced by the intermediate density band observed after one generation and the two distinct bands (one of intermediate density and one matching the lighter nitrogen isotope) observed after two generations, which confirmed that the conservative and dispersive models of DNA replication did not apply.
Key Points from the Experiment
- In the conservative model, original DNA strands stay together while new DNA molecules are composed of two new strands.
- The semi-conservative model predicts each strand of DNA serves as a template for a new complementary strand, resulting in molecules made of one old and one new strand.
- The dispersive model suggests interspersed segments of old and new DNA in both strands of the replicated DNA.
The correct answer to the question 'Meselson and Stahl's experiments proved that DNA replicates by which model?' is b) semi-conservative model.