Chromosomal Mutations: Aberrant Euploidy - Online Tutor, Practice Problems & Exam Prep

Aberrant Euploid

So the chromosomal mutations, what are they? That's mutations referring to entire chromosome sets. So this can be a mutation that describes the change in chromosome structure. So, you know, how big it is, how small it is, how many genes it has on it, and or it can be the number of chromosomal copies. So we're not talking about individual gene mutations, we're talking about the entire chromosome and that being mutated to more copies or having a weird structure.

Now, there are 2 types of chromosomal mutations. The first is aberrant euploidy, which is what we're going to talk about. This involves changes to the whole set of chromosomes. For instance, if every single one of our chromosomes had an extra copy on it. It's the whole set of chromosomes. It's not just one, it's the entire set. So, aberrant euploidy. And then there's a second type, which is aneuploidy, and this involves changes to a part of a single or a few chromosomes. For instance, like Down syndrome, which has an extra copy of chromosome 21. So that would be an example of aneuploidy because it's only affecting that one chromosome and not the entire set of chromosomes in an organism.

Now these videos are going to be heavy in vocabulary. Right? I'm not going to be walking through math or anything like that, but it's going to be a lot of vocabulary words that you're and they're sort of just slightly different. It's going to be hard to memorize them, but you're just going to have to memorize these vocabulary words to understand these chapters. The first one, the first vocabulary word is euploid, which is where we get this term from up here, aberrant, euploidy. And euploid describes organisms with multiples of the basic chromosome set. So humans are diploid. Right? We have 2 copies of every chromosome. Well, we would be described as euploid or an individual would be described as euploid if they had 3 copies of every chromosome set. And it can contain more or fewer numbers.

Now you may say, oh my gosh. How do organisms even survive like this? Well, a lot of times, these are things happening in plants, which are a little more flexible with their chromosomes than humans are. Humans are pretty much, you know, we have to have this chromosome set, with a few exceptions. But it does actually exist in some animals, including amphibians. Amphibians commonly have euploid species. This is actually a common thing where the entire chromosome set either has extra chromosomes or fewer chromosomes.

Now, there's a special term for monoploid, which is a normally diploid organism that contains only 1 chromosome set. So if humans if there was some individual who just lost half of their chromosomes, and so only had one copy of every chromosome instead of 2, we would call them monoploids. And this is different from haploid. Right? Because haploid, they have 1 chromosome set, but they're supposed to. That's what they're supposed to have. Whereas, monoploids are supposed to have 2 copies, but they lost one of every chromosome and so now they only have 1. So there are 2 different terms and it's important to understand the difference.

Now for some of the organisms who do this, who are things like, bees, wasps, ants, can be monoploids. And when they are, they can undergo this process called parthenogenesis. And this is the development of an unfertilized egg. So this is just an egg. It contains half the chromosome set, so it would be a monoploid. Right? It contains or haploid. It contains half the chromosome of what it should of a diploid organism, but it actually develops without fertilization. So it should be diploid. Right? You have an egg, it's haploid, and you should get a sperm that's haploid, and they should come together, fertilize, and create that diploid organism. Well, in parthenogenesis, what happens is you have that egg and it's haploid, but it doesn't get fertilized, yet it still develops into an organism. And that organism is monoploid, because the species is diploid, but that individual actually only contains half of that chromosome set. These are examples, some bees, wasps, ants. These are kind of colony animals type things, or colony insects anyway. So, that is parthenogenesis.

Autopolyploidy

Okay. So now, let's talk more specifically about autopolyploidy. Autopolyploidy typically results in triploids. Not always, but most often, they are triploids. Usually, autopolyploid individuals are sterile. This is because their gametes will receive either 2 or 1 chromosome from each pair. Let's visualize this: they're typically triploid, so they have one chromosome here that's triploid, one here that's triploid, and one here that's triploid. When this undergoes meiosis to create these gametes, what happens is that some of the daughter cells will actually end up with 2 copies, and others of the daughter cells will end up with one copy. Because they started out with 3, it's very unlikely that only one cell will get all 2. Usually, what will happen is that it'll get 1 here and 2 here and maybe 2 here and 1 here, so you end up with this mix where some of the chromosomes have 2 copies and some of them have 1. This creates a gamete that is just not viable. So when it undergoes fertilization with a normal gamete, sometimes it's going to have some triploid, it's going to have some that end up as diploid, and it's just going to be very confusing. Right? And so the gamete typically doesn't survive, and typically, autopolyploids are sterile.

Whenever there are mixed numbers of chromosome sets, so some chromosomes have 2 copies, some have 1, some have 3, this is called aneuploidy, and we're going to be talking about this a lot. Remember, you can go back to the previous video; this was one of the different types of chromosome mutations, the one we're not talking about yet. But, this is when you have a mixture of diploid and haploid chromosomes or can even be triploid. Right? Any kind of unusual mixture of a chromosome set, because not all of these triploids here will segregate equally. Right? There are 3 of them, so sometimes 2 will go to one, and sometimes one will go to another.

There are many classes of autopolyploids. You have monoploids, which use a haploid cell meant for fertilization as an embryo. We talked about this before with the bees and the wasp. This is the organism that develops from parthenogenesis. You can have autotriploids, which are triploid for each set. An example of this is bananas; if they have 40 chromosomes, all 40 of them have 3 copies. And you can also have autotetraploids, which again, are 4n (where "n" refers to the basic number of chromosomes), indicated by 'tetra' for four. We can sometimes see this in plants such as crops or even large flowers, because typically, this results in a larger size. Autopolyploidy often results in larger size because you have the entire chromosome set having multiple copies. And so, in the organisms that can survive with that, which is kind of rare, but in the organisms that can, they are typically just bigger organisms. They have extra chromosomes, they are producing extra of every gene they have, and if they can survive doing that, which some plants and some amphibians can, they are typically just bigger organisms. Very common.

So here are examples: you have a monoploid, where that one chromosome is used as an embryo without fertilization. Here's an autotriploid where you have 3 copies of every set; we've seen this before, but essentially, that's the example. So this is the autopolyploidy. So with that, let's turn the page.

Allopolyploidy

Okay. So now let's talk about allopolyploidy. Allopolyploids typically are plants that are hybrids of two or more species. Usually, these are sterile, and most of these are synthetically created for crops. Examples of these types are cotton and wheat. So, what does this look like? Here are our original organisms. They have one copy, or they have two copies of each of their chromosome sets. But what happens is that somehow, usually through some kind of genetic manipulation, these are fused together, and what you get is you get combinations. You get the red chromosomes here and the black chromosomes here. So now you have allopolyploids, right, because they have chromosome sets from different organisms. It could also be where if you got an extra chromosome here and an extra chromosome here, but they came from different regions. So this red chromosome would come from this organism, and this black chromosome would come from this organism. It's a little different than how I've drawn it, but you have two choices here. Right? You can get a mixture of these two chromosome sets, or you can get what I showed before in that first video with extra chromosomes from that individual. So this would be where we were doing it here. Here's the blue chromosome. Obviously, that's going to fuse this way. But you could get a light blue chromosome, for instance, from this organism that's not perfectly the same, but close enough, and it would come over here. And the same for here. You could get the black chromosomes going here and creating this big fusion organism, or you could get a sort of gray chromosome coming from this blue cell to be here. Either way, it's allopolyploidy. Pretty much allopolyploidy just means some kind of mixture of two chromosome sets from different species. So it can be that they're fusing together those two chromosomes. It can be donating a set of chromosomes from one individual to another, but essentially, this is an example of allopolyploidy. So here's another one with the red and the blue. But they're so little I figured I'd just throw them in here at the end.

Versus Endopolyploidy, these are diploid organisms, but certain cells are polyploid. This can describe some humans. There are liver cells in humans that actually have different amounts of chromosome numbers, so we can call those people endopolyploid. This also happens in the gut of mosquito larvae, where the majority of the mosquito has one set of chromosomes, but in the gut of the larva, some of the cells have extra chromosomes, and also in flowering plants. But essentially, this is where the majority of the organism is diploid, but then a few cells are triploid.

And then finally, there's this chemical you may see in your book. I don't know how to pronounce it, colicin, anyway, this big C word here. This is a chemical that you can put on cells in a laboratory setting to induce nondisjunction. Now, I don't know if you've heard this word, you may have or may haven't, depending on what order you're kind of watching these videos in, but nondisjunction just means that the chromosomes fail to separate properly during meiosis. So if you have a cell here with two chromosomes, nondisjunction would be if in the daughter cells, if two of them went here and none went here. That would be nondisjunction. It could also be if you have right? And in the daughter cells, you have two, so three go here, or two go here, and one goes here. Either way, they're not separating equally, so that is nondisjunction. So this chemical can actually induce that in a laboratory setting in case you ever need to study any of these processes. So with that, let's now move on.

Which of the following chromosomal mutations increases the amount of genetic material from all chromosomes?

• A. Aberrant Euploidy
• B. Aneuploidy
• C. Monoploidy
• D. Tetraploidy

True or False:Autopolyploids contain multiple chromosomal sets from two closely related species

• A. True
• B. False

A species has 2n = 20. How many chromosomes will be found per mutant cell in an autotriploid organism.

• A. 10
• B. 20
• C. 30
• D. 60