Pearson+ LogoPearson+ Logo
Start typing, then use the up and down arrows to select an option from the list.


Learn the toughest concepts covered in biology with step-by-step video tutorials and practice problems by world-class tutors

6. Chromosomal Variation

Chromosomal Rearrangements: Overview



Rearrangement Overview

Play a video:
Was this helpful?
Hi in this video, we're gonna talk about chromosome rearrangements and overview. So chromosomal rearrangements describe changes in chromosome structure. So this is usually focusing on one chromosome but that their um something's happened to a portion of its been deleted or inverted or duplicated. Something's happened weird with the structure. And so there can be many types. Some I just mentioned deletions, duplications, but there are also these special terms called trans locations and inversions. And we're going to go over each of these in their own topic. But typically we refer to no matter which type of rearrangements happening. We name them based on their current to the central mirror. Remember the central mirror? If you draw a chromosome, it's kind of it's usually drawn right here. But we actually know that the central mirror doesn't have to be located in the middle. It can be located at the end located at the other end located slightly off center center mirror can be located really anywhere in the chromosome. Um and so we say that these rearrangements are a centric chromosomes. If the chromosome lacks a central mere due to some kind of chromosome rearrangement, So say that there was a deletion and it deleted this part of the chromosome. Well, that would lose that centrum here and we would say that's an a centric chromosome. There's other types of rearrangements called die centric chromosomes and these are chromosomes with two centrum ears due to some kind of rearrangement. So you can imagine if there was some kind of trans location here where this part of the chromosome went over to this side. What you would end up with is a chromosome with two centimeters and that would be a di centric chromosome. Now die centric chromosomes have a really unique situation happened to them during division. Because if you remember from when we talked about cell division, whenever you've learned about cell division, how do the chromosomes actually separate into their daughter pairs? Daughter cells? Do you remember the central mirrors? Right? Like those micro tubules come out of the sides of the cell and they attach onto the central mirrors to pull those chromosomes to the opposite pole. But if your dia centric chromosome, you can actually have two central mirrors. And those micro tubules can attach in opposite ways and then pull it and it kind of gets stuck. And that is called it an affair bridge. When a dia centric chromosome is pulled to opposite poles during an a face. So those micro tubules come out, each one's grabbed onto a different side of that centrum here and it's pulling it. But it's like just ripping that DNA apart, right? Because it's pulling it and it but it's both sides are pulling it in opposite directions. So here's an example. Here's your central mirror you have, you're a centric chromosome which is going to be, you know from like here to here where it's missing that central mirror and you have your dia centric where you have two copies or two centimeters Now there are two rearrangement types. We say that there are unbalanced three arrangements where there's a change in gene dosage. And this usually occurs by deleting a gene on one chromosome or duplicating it. So you're either losing it or adding it. So there's some kind of gene dosage change. And therefore we call that unbalance. Then the opposite is going to be balanced. And this is when there's just there's no change in the dosage, nothing's happening, nothing's being deleted or added. But instead the gene order is changing. So these occurs through inversions where it just inverts the sequence or trans locations. So let's let's look at an example back up. So you can see, so here's your normal and you have these homologous pairs with two alleles on each chromosome for A. B. C. And D. And here's your centrum here. So an unbalanced is when something gets deleted or duplicated. In this case we've deleted the D. A. Will. So this is an unbalanced rearrangement balance, on the other hand is nothing has been deleted or added. But instead what happens is that the the B. And the C. You can see have changed places. And this is changing the gene order. So there's still the same number of genes. It's just the order has uh switched out. So with that let's not move on

What is the name for a chromosomal rearrangement that causes a change in gene dosage?


Inversions cause what type of chromosomal rearrangement?


A chromosome with two centromeres is called what?