The Ames Test - Video Tutorials & Practice Problems

The Ames Test

in this video, we're going to begin our lesson on the aims test. And so the aims test is really just a scientific screening experiment that is designed only to determine if a chemical is a muted gin or not. And so recall from our previous lesson videos that mutations are chemicals that induce mutations in the D. N. A. And so once again the aims test is really only going to determine whether or not a chemical is a mutation. Now down below we have some text and an image that shows you an example of how the aims test can be conducted. And of course in any scientific experiment there's going to be controls groups and there's also going to be experimental groups. And so we have the control plate on the left hand side and then we have the test or the experimental plate on the right hand side. And really once again, the only purpose of this aims test is to determine if a test chemical is a mutation or not. And so you're testing to see if a chemical is a mute agent. And so what you'll see here in this example of the aims test is that minimal media is being used and this minimal media lacks the amino acid histamine. And so there's no history in available on this minimal media auger plate. And so what this means is that only histamine pro to troughs or in other words only his plus cells are going to be able to grow on this minimal media and his minus cells are not going to be able to grow on the minimal media. And so what you'll notice is that on this plates on this minimal media plate that lacks histamine. Over here in the control plate and over here in the test plate we are adding his minus bacteria to these plates. And so the expectation is that these his minus bacteria will not be able to grow because these his minus bacteria require historian to grow and this minimal media player lacks history. And so we expect that all of these his minus bacteria should die and should not grow. And so uh of course within cells mutations can occur spontaneously or naturally or they can be induced. And so the only way for cells to actually appear on this plate is if the his minus bacteria are mutated back to his plus bacteria. And so the expected mutation that we're gonna be adding is expected to reverse the his minus the mutation in the his minus cells and reconvert these his minus cells back into his plus cells. And so what you'll notice is that when you add chemicals to the control plate over here, you add a non mutagenic chemical, a chemical that you know is not a mutation. And what you'll realize is that some colonies will form on this non on this minimal media plate. And these little blue colonies that you see here are his plus colonies and these his plus colonies form from spontaneous mutations. And so what you'll see here is that on this control plate you expect to find very few his plus colonies that form. And the only reason that these his plus colonies form is because they form from only spontaneous mutations that naturally occur. And so it is expected that some his plus I'm sorry some his minus bacteria are going to encounter spontaneous mutations that revert them back to his plus. And so you only expect to find very few his plus on the control plate. Now on the test plate you do the same thing. You add his minus bacteria. And then in this plate you add a test chemical a chemical that you're testing to determine if it is a mutation or not. And so depending on the results uh will uh dictate whether the test chemical is a mute agent. And so if you get results that are similar to the control then you can uh conclude that your test chemical is not a mute agent. Just like the chemical that you added in the control play is not immune agent. And so if the chemical is not immune agent then you would get the formation of very few his plus colonies and these few hits plus colonies. Again they would form from only naturally spontaneous mutations that tend to occur. However if the test chemical that you are adding to these his minus bacteria is indeed a mutation then you will get results that look like this where you get the formation of many many his plus colonies. And so if the test chemical is indeed a mutation then what you'll get is the formation of many his plus colonies that form and these many hits plus comedies that will form from both spontaneous mutations that are natural but they will also form from induced mutations that are induced by the chemical mutation that you added. And so basically what we're saying is that we can determine if this test chemical is a mutation or not by the number of colonies that form. If there are many many many hits plus colonies that form then we know the test chemical is a mute agent. Whereas if there are not many his plus colonies that form and the plate ends up looking like the control plate. Then we can conclude that the test chemical is not a mutation. And so again it says the test chemical is a mutation if and only if many his plus cells grow but it will not be a mutation is very little to no His plus cells grow. And the number of colonies forum also reflects the immunogenicity or how mutagenic the mutation is. And this relationship is the more colonies that his plus colonies that grow. The greater the immunogenicity is of that mutation. And so this year concludes our brief introduction to the um aims test and how the aims test is used to determine if a test chemical is a mutation or not. And we'll be able to get some practice applying these concepts of the aims test as we move forward. So I'll see you all in our next video.

Ames test is a method to:

• A. Test error rate in DNA replication.
• B. Characterize mutation types.
• C. Test mutagenicity of potential hazardous chemicals.
• D. Test proofreading capacities of DNA polymerases during replication (or PCR).

During an Ames test, if the test plate has only a few colonies grown on it like the control plate, this means that:

• A. The chemical is a carcinogen.
• B. The chemical is a mutagen.
• C. The chemical does not cause mutations.
• D. The cells are resistant to mutations.
• E. None of the above are correct.

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.