Okay. So now, we're going to go through and talk about mutations and the different types of phenotypes they cause, and what all the terminology is used to discuss mutations and phenotypes. So the fourth way to classify mutations is their effect on protein activity and how that affects the phenotype of the organism. So, there are two classes of mutations, loss of function and gain of function. And if you were to take a guess at what that meant, you would probably get it. Loss of function means that the protein's activity is losing its normal function, whereas gain of function means that it is more efficient, has higher activity, it has gained functional ability the protein has. And so, there's one type of loss of function called a null mutation, and that means that there's a complete loss of function. This protein is not at all active. So loss of function can just mean it has weaker activity, but a null mutation is going to be it's completely out of the game. It's not doing anything. 0% function. So that's the first way. You have visible mutations. Obviously, these are going to be mutations that you can see physically, so these are affecting the phenotype of the organism. Couple different classes, you have nutritional ones, which can cause a loss of ability to synthesize some type of amino acid or vitamin. So we all need different amino acids and vitamins to live and our body synthesizes some of them, or we consume them and our body breaks them down into what we need. There are mutations in any of those processes and synthesizing what we need or breaking down what we need, then that results in a nutritional mutation. Now you can't just look at someone and see that, but they do typically, the people with nutritional mutations, do typically have very severe phenotypes. And if they're not getting that nutrient, that's a nutrient deficiency, and that results in some kind of phenotype you can visibly see. A second type is behavioral mutations. These are really hard to study in a lab because it's behavior and behavior is very different for individuals. But there are some mutations that can affect, changes in behavior of an organism. And, obviously, you're going to see that because it's behavior and they're acting a certain weird way. Now there's a certain class called conditional mutants, and these are only detectable under certain conditions, meaning that they are active, so they can cause harm, under certain conditions only. And under normal conditions, they don't cause harm. So the best example of this that your book uses is temperature sensitive mutants, and these have been designed by scientists to study in various organisms like fruit flies, worms, and even mice. And, essentially, at some higher temperature, generally, how these work, is that at normal temperatures, these are expressing wild type levels of gene and protein. Right? Those are being expressed, and you have wild type levels. At some higher temperature or some lower temperature, those temperatures then mess up the protein, and therefore, you can see the mutant phenotype. Because now that protein is not being produced correctly, it's being produced in this mutant temperature sensitive way that is causing some kind of phenotype on the organism. So conditional mutants are a lot of times used by scientists to study various types of mutants, which wouldn't be able to be studied otherwise. Then we have lethal mutations. These are mutations that cause death of the organism. So lethal mutations are often studied by scientists and conditional. Right? Because if you are trying to study a lethal mutation, if you put that into an organism, that organism is going to die, and it's never going to develop. Right? It's never going to you mix an egg and sperm together. It's going to die as a fetus. But if you make it a conditional mutant, and you can grow it, that protein will be expressed normally. That organism will develop in utero. After it's born, you can then move it to a different temperature and study the effect of the phenotype, under a condition where the organism is still alive. So but lethal mutations cause death if they are present. And then finally, the least exciting, is the neutral mutations, which are mutations that have no observable effect on the organism. Now, if you had to guess, some of the mutations that we've talked about before, especially the ones that maybe affect codons, which type would you say is most likely a neutral mutation? Right. That would be a silent mutation. Right? Something that changes one codon to another codon, but that codon still codes for the same amino acid. Most of the time, neutral mutations are not affecting codons at all. Sometimes they do, and they're found in places like introns, for instance, that aren't coded anyway, and they have no effect. And so neutral mutations have no effect on the organism, whether because they're in coding regions but code for the same amino acid, or because they are non-coding regions and therefore it doesn't really matter for the organism whether or not it gets mutated. So here, we have an image that is, looking at the difference between loss of function and gain of function. You scroll up so you can see. So here we have wild type, and you can see there are two alleles. Right? For each gene, there are two alleles. So both the wild types are producing the same number of these, like, little allele that produces the same, and then the mutant allele you get a decreased amount of black circles. For the gain of function, you have one allele that's wild type. And for a mutant, you can have a bunch of gain of function, which will create a lot more little black circles. Now if you had a null mutation, there would be no black circles. And if you had a mutation in both alleles, that would obviously be more severe because both alleles would be producing these altered amounts of little black circles, and not just one that has a mutation. Now, there's a fifth way to classify mutations based on their effect on individual alleles. So again, lots of vocab, sorry for this, but we just got to get through all the vocab and then we can get some more interesting stuff. So, we have hypermorphic mutations. And hypermorphic mutation is a loss of function mutation, and this still produces some type of functional protein. So this would be here. This would be called a hypomorphic. The reason is because there's still protein present, but it's probably weaker than the normal amount of protein that's present. Haploinsufficiency, which you may have heard before, probably a while ago now. But haploinsufficiency describes when there's a wild type allele still left. So only one of the alleles are mutated. But the one wild type allele is not enough. It can't provide enough gene product. So the organism still appears mutated. So the other is usually a null or generally loss of function. And when it is, you only get half the gene product, and that's not enough to create a normal phenotype of the organism. We have dominant negative. Dominant negative is when you have a mutant allele and a wild type allele. And the mutant allele, whatever is produced from it, produces some kind of protein that blocks the production of the other. And so, dominant negatives are used a lot by scientists to study various genetic things. But, essentially, you have a wild type and a mutant, and that mutant creates something that, sort of, shuts down that wild type from functioning. So, again, that organism, even though it has a wild type allele, looks very much mutant. Now we have hypermorphic. This is kind of the opposite to hypo that we talked about above. Hypermorphic gain a function that produces a more efficient protein than wild type. So that would be this situation here. And then we have neomorphic mutations, which is generally a mutation that produces some kind of novel phenotype. So it's not I mean, it's a mutant phenotype, but it's not necessarily worse off. It could be potentially better for the organism, but it's generally a different phenotype than we've ever seen before with this gene and this allele. So here we have wild type alleles. Right? They have a 100% activity. If there is some type of mutant here, it's a null allele if there's 0 activity from this one allele. It's hypomorphic if there's 30% activity, and then it's hypermorphic if there's 160% activity. Right? So these are kind of the differences between how they're affecting alleles and the phenotype. And then finally, the last class of vocab. I know you probably have like a whole sheet written down of vocab words, but this is the last one. It's the sixth way, and it's by their suppression activity. So there are mutants called suppressor mutants, and these mutants are or these mutations cause the suppression of another mutation. So there are two mutations and one of them causes the suppression or the block of another. So suppressors, there are two types, intragenic. Notice here it's the 'tra' that separates this from the next one. Intragenic, where the mutation is found in the same gene as the mutation being suppressed. So if we have a intra, all right, a 'tra', then you have a mutation here and a mutation, here, and this one is blocking that mutation, and it's in the same gene. Then, you have intergenic, this is going to be 'ter'. And this blocks, or is a mutation in a separate gene, than the mutation being expressed. So it can even be on a different chromosome. So we'll do this. So we have a mutation here and a mutation here. And this one comes out from even a different chromosome and causes suppression of this second mutation. Blocks it. So suppressor mutations exist. They're important. Sorry for all the vocab. I truly am. I wish it were easier. But hopefully, the majority of them kind of make sense into why they're called that way. But if not, just keep reviewing and making sure that you know what the differences are between these vocab words. Because if you don't, then it's going to make answering some of the word problems that I'm sure you'll get much more difficult. So with that, let's now move on.
17. Mutation, Repair, and Recombination
Types of Mutations
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