In an experiment employing the methods of the Ames test, two strains of Salmonella are used. Strain A contains a base-substitution mutation, and Strain B contains a frameshift mutation. Four plates are prepared to test the mutagenicity of the compound ethyl methanesulfonate (EMS). Plate 1 is a control plate with Strain A and S9 extract but no EMS. Plate 2 is also a control plate and contains Strain B and S9 extract but no EMS. Plate 3 contains Strain A along with S9 extract and EMS, and Plate 4 contains Strain B, S9 extract, and EMS.
What event is being detected by growth of a colony on any of the four plates?

Question

What event is being detected by growth of a colony on any of the four plates?

Accepted Answer

Hi, everyone. Let's check our next question. It says the Aimes test uses two salmonella strains. Strain A with a base substitution mutation and strain B with a frame shift mutation and four plates to test the mugen of Ems, two control plates have no EMS and two experimental plates have ems with each strain. What is the significance of the presence or absence of a colony on any of the four plates? Choice A, the absence of a colony on the experimental plate indicates that EMS is meto choice B. The presence of a colony on the experimental plate demonstrates the effectiveness of antibiotics in treating bacterial infections. Choice C the presence of a colony on the experimental plate indicates that EMS is muto or choice D the absence of a colony indicates the degree of toxicity of the compound being tested. So let's think through a brief overview of our aims test in the Ames test. We start with a mutant stream of salmonella that can't grow in a medium without histadine, you've mutated it, it's lost its ability to synthesize its own histine. You then expose this stream to a potential mutagen to a substance that you want to test whether it will cause DNA mutations. You then grow the exposed strains on medium without his. Because you know that if your substance, you're testing does mutate DNA, some of those colonies will have a reverse mutation that will regenerate the ability to synthesize their own histamine. So in this case, on the control plates, you will see no or very few colonies, theoretically, none of them will grow. Since your mutant strains don't have the ability to synthesize histine. But you can have random mutations that occur. And if a random mutation regenerates that ability, it will grow as a colony, but that's not a really common event. So you aren't going to see very many colonies. Then in your experimental plates, it will depend on the mutagen of your test substance. If it doesn't cause mutations, you will see the same result as your control plate no or very few colonies. If it does cause mutations, you will see more colonies than on the control plate since you'll generate some reverse mutations. So let's look at our answer choices and see what reflects that. And we see that Choi C says the presence of a colony on the experimental plate indicates that ems is mugen. So as we said, the experimental plates depend on the mediagenic of test substance. And when you have colonies on these experimental plates, it means that your substance was a mugen. We'll just look at our other answer choices to understand why they're not correct. Uh Two we can eliminate right away. Choice B says is talking about the effectiveness of antibiotics but that's not what the A S test looks for. So choice B is not our answer. And Choice D talks about the degree of toxicity of the compound. Again, that's not the purpose of the aims test. That's not what you're looking for. So choice D is not our correct answer. Finally, Cho A says the absence of a colony on the experimental plate indicates that EMS is muto but of course, this is opposite from what we expect. If there are no colonies on the experimental plate, that would indicate the strains remained without that ability to synthesize histidine. The EMS was not me agentic. So that's why choice A is not our answer. So again, what is the significance of the presence or absence of a colony on any of the four plates? Choice C the presence of a colony on the experimental plate indicates that the EMS is Mugen. See you in the next video?

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Key Concepts

Ames Test

Types of Mutations

Mutagenicity