Chromosomal Rearrangements: Inversions - Online Tutor, Practice Problems & Exam Prep

An inversion is a chromosomal mutation where a segment of DNA is reversed, maintaining the same genetic information but altering its order. There are two types: paracentric inversions, which do not include the centromere, and pericentric inversions, which do. Inversions can lead to an inversion heterozygote, where one chromosome is normal and the other is inverted. These mutations often arise from an inversion loop during meiosis. Scientists utilize balancer chromosomes, which contain multiple inversions, to prevent crossing over and study genes without altering their stability.

Inversions

Hi. In this video, we are going to be talking about inversions. Okay. So an inversion is when the chromosome keeps all the same genetic information, but the order of it is switched around. So an inversion is when the orientation of a segment is reversed or flipped. Now there's going to be 2 types. We have the paracentric inversion and the pericentric inversion. Now these are really similar, so make sure you don't mix them up. Para and peri, so para- and peri-. Now para- is going to not include the centromere. So, an inversion that happens outside of the centromere. Peri- includes the centromere. So when the segment that's being flipped also includes the centromere. So let's look at the example. So if we had a chromosome here, we'll call it A B C D, this is going to be our normal version, and it has a centromere right here. A paracentric inversion is when the part that's being flipped, which in this case is C and D, there's no centromere. Right? Like, we can cut here and flip this chromosome around and make it normal, and we can cut there and flip it around and make it paracentric. Right? The DNC, we flip it around, there's no centromere involved. Pericentric is when there is a centromere involved. So you can see that the C and the B, they are inverted. Supposed to be A B C D, but instead it's A C B D, but this inversion includes the centromere. So when it flips, we have the centromere included. So, that's the pairing. Now, when this happens, what we usually get is one normal chromosome and then one inverted chromosome, either paracentric or peri-, it doesn't matter. Often we get one normal, one inverted. And what we call that is an inversion heterozygote. Okay. So we have one normal and one inverted. Now this heterozygote, we typically think of actually referring to genes or alleles, and we think heterozygote we see we think this. Right? One dominant and one recessive allele. But, that is not what this means. Right? So, if we look at these above, if we take this and this, or let me just write it again here. So, if we have one chromosome that looks like this, one normal, and one that looks like this, Or, hold on. I wrote that wrong. Let me write my letters correctly. C B D. There we go. So, if we have one normal and one pericentric, we can see that actually in this case, all of the alleles are dominant. Right? We have this homozygous dominant for both chromosomes. Right? So, it's not that the alleles are heterozygous, it's just that the chromosomes are heterozygous. Now, how do inversions happen? Well, a lot of times what happens to them is an inversion loop forms. And an inversion loop literally kind of just looks like a ribbon. And you can see right here during this part, this section and this section can easily flip over. Okay. And, sometimes you will see it drawn like this. Right. And during this section, you can imagine how easily it is for a gene that is here to get put really close to a gene that's here. Okay. So these are examples of inversion loops, and that is what forms and what allows these inversions to take place. Okay. So the twisting of one end pairs with an uninverted one or pairs with an uninverted end, and that ends up causing inversions. Now, if scientists want to study inversions, then what they often do, or they want to study genes in general, not just inversions, just any kind of gene. So a geneticist wants to study that. But they don't want any kind of crossing over. They really don't want to mess with the gene. They really want to keep everything as stable as possible. One of the things that they'll do is use a balancer chromosome. Now, a balancer chromosome is a chromosome that scientists have created. It contains a ton of inversions in it. Just inversion after inversion after inversion. And the reason that it does is because it wants to prevent crossing over. So it suppresses crossing over, so that scientists can study a gene or a chromosome without crossing over occurring. So, balancer chromosomes are inverted chromosomes that scientists have made to help in their studies. So, here is an example of an inversion heterozygote. We can see we have one normal chromosome. We have A, B, C, and D in their correct order with the centromere here. And we have one inversion A, C, B, and D. Now note, this is heterozygotes referring to one normal and one inverted chromosome and has nothing to do with the alleles, which in this case are all homozygous dominants. Okay, So make sure you don't mix that up because students get really confused about that because they hear heterozygous and they're already thinking alleles. In this case, inversion heterozygotes focus on chromosomes. Okay, so with that, let's move on.

A person has a WT chromosome with the following segments. A B C • D E F G H. Which of the following shows how the chromosome would look after an paracentric inversion?

• A. A B C • D E F G H
• B. A B E D • C F G H
• C. A B C • D G H
• D. A B C • D G F E H

A person has a WT chromosome with the following segments. A B C • D E F G H. Which of the following shows how the chromosome would look after a pericentric inversion?

• A. A B C • D E F G H
• B. A B E D • C F G H
• C. A B C • D G H
• D. A B C • D G E F H