The fluctuation test performed by Luria and Delbrück is consistent with the random mutation hypothesis. Briefly describe their experiment and identify how the results match the prediction of the random mutation hypothesis. What would have to be different about the experimental results for them to agree with the prediction of the adaptive mutation hypothesis?

Key Concepts

Random Mutation Hypothesis

The random mutation hypothesis posits that mutations occur randomly and independently of an organism's exposure to environmental pressures. This means that genetic changes arise without any foresight or adaptation to specific challenges, such as antibiotic resistance. In the context of Luria and Delbrück's experiment, this hypothesis predicts that the number of resistant mutants in a bacterial population would vary widely, reflecting the randomness of mutation events.

Luria and Delbrück Experiment

Luria and Delbrück conducted a series of experiments using E. coli to test the random mutation hypothesis. They exposed bacterial cultures to a bacteriophage and observed the emergence of resistant mutants. Their results showed a significant variation in the number of resistant colonies across different cultures, supporting the idea that mutations occurred before exposure to the phage, rather than as a direct response to it.

Adaptive Mutation Hypothesis

The adaptive mutation hypothesis suggests that mutations can occur in response to environmental stressors, allowing organisms to adapt more effectively to their surroundings. If Luria and Delbrück's results had shown a consistent pattern of resistance that correlated with exposure to the bacteriophage, it would indicate that mutations were not random but rather a directed response to the selective pressure, thus supporting the adaptive mutation hypothesis.