Question

The fluctuation test performed by Luria and Delbruck is consistent with the random mutation hypothesis.

Complete a brief outline of their experiment.

Rank the steps of the experiment from the first to the last.

1. they split the culture into smaller cultures.

2. they took a large culture of a bacterial strain susceptible to infection by a bacteriophage.

3. they determined how many colonies grew on each plate.

4. they plated samples containing equal numbers of bacteria from the cultures on petri plates containing the bacteriophage.

5. they allowed the cultures to double for multiple generations.

Answer 1

Answer:

they took a large culture of a bacterial strain susceptible to infection by a bacteriophage.

they split the culture into smaller cultures.

they allowed the cultures to double for multiple generations.

they plated samples containing equal numbers of bacteria from the cultures on petri plates containing the bacteriophage.

they determined how many colonies grew on each plate.

There were two theories on how mutation occurs

Adaptation or induced mutation theory – mutation can occur only in the presence of a mutagen

Spontaneous or random mutation theory- mutation is a random event that can happen in the presence or absence of mutation

Salvador Luria and Max Delbruck performed an experiment to prove how mutation occur

Set up:

A single wild type ( is sensitive to T1 bacteriophage and will get lysed by the virus) E coli culture was divided into several subcultures and allowed to divide for four generation. In the fourth generation the scientist’s added T1 bacteriophage. If all of these cells are of wild type they will all be lysed by the phage and if they are mutated then they will be able to be resistant to T1 phage and form colonies. Here T1 phage is the mutagen and is present only in the fourth generation.

If induced mutation theory is correct then mutation will occur only in the fourth generation and the mutation rate will remain the same for all the cultures. If random mutation theory is correct, then mutation can occur irrespective of the presence of T1phage, so mutation will be present in any of the four generations and the rate of mutation will differ. After this experiment it was observed that spontaneous theory is correct (even though this result is still open for debate in scientific community)