Genetic 342 A&B Kenneth G Wilson Professory of Botany

The Actors

• Matthew Meseson
• Franklin Stahl
• Their meeting (Jim is Jim Watson I think )

The Hypothesis - 3 possible Models for Replication (from text)

• Semi-conservative Replication

The Alternative Hypotheses

• Conservative Replication
• Dispersive Replication

The Technology to test the hypothesis

• Isotopic Labelling - What isotope would you use?
• Cs-Cl Centrifugation
  

The Test and independent verification

• 1958 Matthew Meselson and Fanklin Stahl proposed and tested the 3 models of DNA replication.
• They grew bacterial cells in media made heavy nitrogen (15N) and then transfered these cells to media with light or natural nitrogen(14N). The results are shown in Figure 23-3 (Woolf).

• After one round of replication the Conservative Model is proven false
• After a second round of replication the Dispersive Model is proven false.
• Thus by the scientific method the Semi-Conservative Model is assumed true.

Let us review these results.

Please note that this is a beautiful experiment that rules out all reasonable hypotheses.

Herbert Taylor did essentially the same experiment at the same time (1958) in beans. He used a different label or isotope-namely Tritium (H3) and a different assay -namely radiography.

Today we would use 5-bromouracil for both of these experiments.
This is the theory.
This is the actual .

This is our friend Oliver the parrotlet, Oliver is a true parrot, the smallest in the world.