Multiple Choice
During an Ames test, if the test plate has only a few colonies grown on it like the control plate, this means that:
16. Microbial Genetics
The Ames Test
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In the Ames test, why do some His+ colonies form even when a mutagenic chemical is not used?
A
Some bacterial cells will have spontaneous mutations which turns them from His- to His+.
B
Some bacterial cells will have induced mutations which turns them from His- to His+.
C
The minimal media induces mutations changing some of the His- bacteria into His+ bacteria.
D
The cells used to start the experiment were not entirely His- cells.
Verified step by step guidance1
Understand the Ames test: It is a biological assay to assess the mutagenic potential of chemical compounds. It uses strains of bacteria that are unable to synthesize histidine (His-).
Recognize the role of spontaneous mutations: Even in the absence of a mutagen, spontaneous mutations can occur in the DNA of bacteria, leading to a reversion from His- to His+.
Consider the genetic variability: Bacterial populations can have genetic variability, and some cells might naturally revert to His+ due to random mutations.
Acknowledge the possibility of contamination: The initial bacterial culture might not be entirely His-, meaning some His+ cells could be present from the start.
Evaluate the experimental conditions: Minimal media can exert selective pressure, potentially favoring the growth of any spontaneously mutated His+ cells, making them more noticeable.
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