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UC MUSEUM OF PALEONTOLOGY
Understanding Evolution
Your one-stop source for information on evolution
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The Lederberg experiment
In 1952, Esther and Joshua Lederberg performed an experiment that helped show that many mutations are random, not directed. In this experiment, they capitalized on the ease with which bacteria can be grown and maintained. Bacteria grow into isolated colonies on plates. These colonies can be reproduced from an original plate to new plates by “stamping” the original plate with a cloth and then stamping empty plates with the same cloth. Bacteria from each colony are picked up on the cloth and then deposited on the new plates by the cloth.
Esther and Joshua hypothesized that antibiotic resistant strains of bacteria surviving an application of antibiotics had the resistance before their exposure to the antibiotics, not as a result of the exposure. Their experimental set-up is summarized below:
So the penicillin-resistant bacteria were there in the population before they encountered penicillin. They did not evolve resistance in response to exposure to the antibiotic.
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Read more about how mutations factored into the history of evolutionary thought
Learn more about mutation in context:
- Evolution at the scene of the crime , a news brief with discussion questions.
- A chink in HIV's evolutionary armor , a news brief with discussion questions.
Find lessons, activities, videos, and articles that focus on mutation.
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