In this video, we're going to begin our lesson on mutant detection, or the methods that scientists can use to detect the presence of mutants. Now, scientists can identify or detect mutants by using two different methods of detection. The first method is the direct selection of mutants, and the second method is the indirect selection of mutants.
In the method for direct selection of mutants, this method is only going to promote the growth of selectable mutants or mutants that can actually be directly selected for. However, this method will not promote the growth of the non-mutant parents, and so only the mutants will grow, and that makes it very easy for the scientists to select the mutant directly and easily since, once again, the mutant is the only thing that is going to grow.
Unfortunately, not all mutants can be selected for by direct selection. In fact, direct selection does not work for selecting auxotrophs. And so, recall that auxotrophs are going to be mutants that require additional growth factors. The reason that direct selection does not work on selecting auxotroph mutants is that prototrophs, the non-mutant forms, are always going to grow where auxotrophs grow. And so, there's really no way to only allow for the growth of the auxotrophs without also allowing the growth of the prototrophs.
If we take a look at our image down below on the left-hand side, what you'll notice is that this image is focusing on the direct selection of mutants. Notice that this colony that you see here in red represents the growth of the mutant. Notice that there are no other colonies that are forming other than mutant colonies. What you can see here is if we zoom in, only the mutant will grow. The others that are not mutants, notice that they are dead, and you can tell because their eyes have these x symbols through them. Because only the mutant is growing, it promotes the growth of selectable mutants, making it possible to select the mutant directly and very easily. Once again, all you have to do is take that one colony, and that is the mutant you selected for.
Now, direct selection of mutants is really convenient, straightforward, and pretty easy. However, not all mutants can be can be selected for directly. And so those mutants, like for example auxotrophs, which cannot be selected for directly, must be selected for indirectly. And so, this leads us to the second method of detecting mutants, and that is the indirect selection of mutants.
In this process, both mutants as well as the non-mutant parents are going to grow. This means that the mutants that are growing are also going to be growing amongst non-mutants. The mutants have to be indirectly selected for amongst the crowd. If we take a look at our image down below on the right-hand side, what you'll notice is that this image is focusing specifically on the indirect selection of mutants. Notice that on this agar plate both the mutant, which is in red here, and the non-mutant parents are going to grow. And so it makes selecting for the mutant a little bit more challenging, a little more difficult. However, this is sometimes going to be a required process.
What we can say is that if we zoom in, both the mutant as well as the non-mutants are going to grow. The mutant must be selected for out of the crowd. If you can imagine that these mutants are like Waldo from Finding Waldo, with direct selection, it makes finding Waldo or finding the mutant very easy and straightforward since Waldo is the only one that grows. However, with indirect selection, then finding Waldo is going to be a lot more difficult. Finding the mutant will be a lot more difficult because, again, the mutant will grow, but so will non-mutants.
In order to select for this mutant, it must be selected for indirectly using a specific method. What we're noticing here is that typically indirect selection is going to be a more tedious method, and it's only going to be used when it's required for identifying a non-selectable mutant. A non-selectable mutant is a mutant that cannot be selected for directly and so it must be selected for indirectly. For example, an auxotroph.
The indirect identification of the mutant amongst the crowd can be accomplished via a method known as replica plating. We'll get to talk more about replica plating in our next lesson video, to talk more about how this mutant can be selected for amongst the crowd. But here, this concludes our initial introduction to mutant detection through direct selection and indirect selection. And once again, we'll talk more about replica plating in our next video. So I'll see you all there.
