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The Luria-Delbrück Experiment
- The Luria-Delbrück experiment, explores whether mutations occur randomly or whether they are the result of selective pressure.
- To make things simple, the experiment is done by starting off with just one individual who is not a mutant.
- For the first two generations of this 'parent', there is no selective pressure, with pressure only being present in the third generation.
- The most common case is having no mutations, as shown in the case where mutations are Lamarckian.
- In the case of random mutations, you can still get similar results as the case where mutations are Lamarckian.
- If no mutations have occurred, the variance is the same as the mean, and we have a Lamarckian Poisson process.
- On the other hand, there is much more variation in the number of mutants because of mutations happening early in the family tree in random mutations.
- This non-uniform variance indicates that mutations happen all the time, regardless of whether selective pressure is present or not.
- Luria & Delbrück, experiment using E. coli bacteria reveals that there was a lot more variation than expected from a Poisson process.
- In conclusion, Darwinian evolution results in a larger variance in the number of mutants than Lamarckian evolution.
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