Chromosomal Rearrangements: Translocations

Hi in this video, we're gonna talk about chromosomal rearrangements focusing on trans locations. So trans locations, there we go. So trans locations. Um pretty much just describes when a chromosome segment is moved to a different chromosome. So this can be um they can actually just switch parts to separate completely separate chromosomes can switch parts or just one can move to the other. But it's essentially that chromosome being moved to a different location or trans location. Now there are two types. The first type we're gonna talk about is reciprocal reciprocal trans locations. And these are when two chromosomes trade a centric fragments first. Do you remember what a centric means? Right means without centrum ear. So this is a fragment that does not contain a centrum ear in it. And there are three rays that these trans locations are sorted into gammas, right? Because the reason we study these is because they're inherited or they can be. And so when we think about trans locations happening, it's important to understand how that happens. But that's easy enough to just conceptualize, right, It's, you know, a portion of a chromosome without a central mirror is switched with another portion of a chromosome without a central mirror, but that doesn't necessarily do anything unless it's inherited. And so when we talk about these chromosomal aberrations and mutations, we have to talk about them in form of gametes of how their inherited. So whenever this translocation occurs, the way that they're sorted into gametes can be classified in three ways. So when I talk about these, I'm going to talk about the normal chromosomes and the trans located chromosomes. So the first one. And if it doesn't make sense, I'm gonna go over a really detailed image of this. So just hold on, we have adjacent one segregation. And this is sorry about that. There it goes. Um This is when the gametes form have one normal and one trans located. And notice the numbers here. Because you start out with two chromosomes right here we go. And if these to change spots, then you have a normal one trans located, one normal to trans located two. Right? Because these two are the ones that underwent translocation and the numbers actually matter because in one situation you're referring to homologous chromosomes and in another you're referring to non homologous chromosomes. And if it doesn't make sense, there's an image to explain it. But just sort of know that these are how the gametes form in adjacent one segregation. And these are in viable, adjacent to segregation is the same thing. But notice the numbers here are different. You have one normal and one trans location. But these are homologous whereas these are not homologous but they're both in viable because you don't have one full set of chromosomes and then you have alternative segregation and these you have one set of gametes that are both trans located and one set that are normal. And so the gametes are all viable. So let's walk through an example of this. So like I said, we start out with chromosomes, right? We have normal one normal too. And some type of translocation has occurred here, right here here. So now we have a trans located one where this is A B. G. And H. We have a trans located two with E. F. C. And D. And so these are marked by their the letter. So the letters are representing different genes in this case. So we have one chromosome that has A. B. C. Or D. We have another that has E. F. G. And H. And these are two separate chromosomes. These are not homologous, right? Because they have different genes on them. Anything with an A B C. Or D. Is homologous. But these are actually two separate chromosomes, chromosome one and chromosome two. And so there's they have a homologous pair. Right? So if we were drawing these, like how they how we normally see them, you would see them like this. And I guess this is supposed to be red. Hold on E F G H E F G H. So these are the homologous pairs, each one of these, but the black and the red are two different chromosomes. But in this case a translocation has occurred here. Right. These two have switched over and these two have switched over. So now you get in one into two normal chromosomes, right? This one here and this one here and you have to translate located ones, the ones that trans located here and the ones that trans located here. And this is important. So now when you get the gamut or you get the cell essentially what happens is this is what you have. You have one normal is in one and you have to normals into and you have your trans located T. One and T. Two. And if you can just tell by the letters like A B G H A B G H S. T. One, that's how I got that. Same for A. B. C. D. Is in one in one A B C. D. So following the letters here is gonna be super important. Now we are interested in gammas. Right? So first thing that happens in mitosis is these chromosomes replicate. Right? So replication happens and now I have two copies of every single one of these chromosomes. And so now I have eight. Right? And then these have to be sorted into gammas. And like I said, there are three ways to do that. Now. What's important to understand here is that during meta phase which is pretty much what's drawn here. It's it's very complicated and confusing. But meta phase this is meta phase drawing meta phase here. What happens during meta phase? The paired chromosomes line up? So the first thing that's super important is that during mitosis um similar homologous chromosomes pay her up. And so that means anything that is homologous to the other. So anything with the same genes on it is gonna pair up. And normally during normal. My Asus this makes sense because there's only one other option, right? But after a translocation there's actually now multiple options of things that have that can pair up because they're similar. So for instance if we're wondering what can pair up with this here that has A. B. C. Or D. It can now pair up with anything that has an A A. B. Or C. Or a. D. So we compare with this, it compare with this, it compare with this, it compared with this and this. So all of these different pairings are what give us these different names. So let's just take it one step at a time. So we're gonna say we have our A. B. C. And D. So this is our normal one and it's gonna pair with its the normal one. And that's the replicated copy. Then we have our other normal normal too. And it's gonna pair with its exact copy normal too. And the same thing happens down here we have T. One pairing with T. One T. Two pairing with T. Two. So when this forms gamut so these are going to separate and go this way into one gamut and the other side on the other side of the metal faceplate are going to form a second gammy. Right? And so here are the gametes that are formed. You have one with two normals in one and N. Two And you have another one with T. One and T. Two. But the important thing here is that we're looking at the number of genes. Right? So all the genes A B C. D. E. F. G. H. They're all present here. And even in the trans located version you have a. B. C. D. E. F. G. H. You have every gene that you started with. So these are viable because you have every gene that you started with. And so even though there was a translocation occurring and the gene order is very odd in this in this gamut here. Very odd. Right? You have A B. G. H. And E. F. C. D. That's an odd order. But all the genes are there so it's still viable even though a translocation has occurred. Now let's look at adjacent one. So like I said before we're gonna focus on what compare. Right? So in this case we're going to start with um we're gonna say that this one pairs with this one but this one pairs with this one. And so that's what you get here. You get the non homologous ones. So you get in one but you also get T. Two right? T. Two T. Two. Here we go in one T. Two. That's how I got this and that way on the other side you get in one or you get into and T. One. So when these divide into gamma. So this is the meta face plates. So all four of these are gonna go into one and all four of these are gonna go into another. What you get is you get A. B. C. D. E. F. C. D. So you do not have a full set of genes, not full set. This one you have E. F. G. H. A. Bgh. Again you're missing C. D. Not a full set. So this is not viable. Which is what that's supposed to say here, even though it got cut off, not viable and that's adjacent one. Now we say that it's non homologous because in one pairs with T. two so these are not the same number. So this is non homologous and then finally you have the adjacent to which is the exact opposite right? So you have your into pairing with your T. Two and you're in one pairing with your N. Two. And when these go to one cell and these go to another you get two gametes here and if you follow its E. F. C. D. E F. G H not complete. A. B C. D. A B G. H. Again not complete. So these are not viable. So to make sense of this hopefully this does make sense. I realized it's confusing. But the important thing here, I think people get confused in this step how I got from here to here and the reason that I did is because I just paired it up with everything it could pair up with. So in this case A B. C. D. Can pair up with its copy or the A. B. Um C. D. Can also pair up with its um non copy and the same here. So it's a non exact copy it's trans located form. So if you have, let me see here, let me look at a good example. Yeah I'm trying to get a good example here. But essentially you look up and you say A. B. C. D. What can it pair with it compare with the A. B. C. D. It can also pair the A. B. G. H. And the A. B. G. H. Compare with A B. G. H. Or A B. C. D. And you can see this through any of them. So it's just because it makes it more confusing because there's so many more pairings that can happen here. But essentially if you follow it by the number right in one into T. One T. Two it makes it much easier. So I suggest if you get a question like this on the test, the first thing you do is label your normal and your trans located chromosomes. And then you will be easy to just memorize you know these numbers. So adjacent one is gonna be into T. One and N. One T. Two different numbers here because they're non homologous here. It'll be the same and here it will be all trans located and all normal. And that will really be able to help you follow this throughout the entire entire process. But remember the only ones that are viable are the alternative segregation here because they have a complete set of genes. So that is this type of trans location. With that, let's now turn the page.

Okay, so now let's talk about the second type of translocation and this is a robert Sony and translocation and this is a little bit different and it's actually the source of familial Down syndrome which is actually an interesting case of Down syndrome. It's very rare but it does exist. Um and here's kind of the definition of it's a little confusing but hopefully the image will make it clearer. But this is when they're breaks that too short arms of two non homologous afrocentric chromosome. So remember the two short arms here are breaking off. And that leaves two long arms um forming a single chromosome. So instead of having you know these what you end up with two long arms and two short arms from a trans location here. Now there's two forms of this, there's the balance form. And typically in like familial examples of this, this is gonna be the parent and the balance form has this translocation. So it looks like this, but it results in no problem. So there's no phenotype, right? So this this parent doesn't have Down syndrome, they're just carrying that translocation which allows it to happen. And this is because you have both copies, right? You have the big long arms of both copies of chromosomes. And even if the structure isn't right, all the genes are there. So there's really no problems. And the unbalanced form which is usually the child in this familial Down syndrome case that I've been talking about. There's a chromosomal imbalance. So you have this and you have this and now you have too many copies of the same chromosome. So let's go through this um, example, let me back up. So first let's talk about the normal, right? Normally you have chromosome 21 in chromosome 14. So this is going to be the example of inherited or familial down syndrome. And so normally when a normal person I was 21 and 14 and they create a gamut, they get one of each. Right? So you have one copy of 21 and one copy of 14. And this is the gamut. And that's what happens now, I wrote it gray and blue. It could have been green and black doesn't really matter. But essentially, you only get one copy of 21 1 copy of 14. And that's how my oasis works, right? It replicates it divides it and it divides it again. So, your hap Lloyd. So this is hap Lloyd because it contains one copy of 21 1 copy of 14. This is normal. But what happens in robert Sony in trans location that's balanced, Right, it appears normal. But what's happened is you have one copy of 21 and one copy of 14. But there's been a Robert Sony and translocation between the other two forms of the 21 and 14. So the green and the black now are on the same chromosome. So you have two long arms. of 14 and 21 and two short arms Of 14 and 21. Now this person appears normal because they have the long and short arm of each 21 and 14. Right? They have the exact same amount of genetic material as this person. This normal person over here. But the structures are all messed up in different. So this results in 45 chromosomes. And the reason we say this is 45 instead of 46 is because the two short arms are so small and they they're afrocentric so they don't have a centrum er attached to them. So that means during division they're actually just lost. So um end up with one copy of 21 1, full copy of 14 and just the long arms of 14 and 21 as the second copy. But because these small arms here are so small, they don't really contain that much genetic information. And the genetic information they do contain is actually repeat Elsewhere in the genome. So it's kind of just like this region that's not necessary for life. I mean obviously it's important but it's not necessary. And so these people appear normal. But they only have 45 chromosomes, but they contain enough of the genetic material still to appear normal, even though they've lost the short arms of 14 and 21. So when this person creates gametes, their gametes look a lot different than when the normal person creates gametes. So here are the different gametes, they can form, They can form just exactly like the other one did the normal the normal non Robertson's translocation person did they can contain they can have a gamut that contains 21 and 14. And that's here. And this is very normal, right? Like this looks exactly the same. And they have the ability to produce that because you get one copy of 21 and one and 14. And there's a chance you could just get the normal copies. Now there's another option where you need one copy of 14 and 21. But the Robert Sony in translocation actually contains a copy of 14 and 21. So you just get that Robert Sony in translocation, right? Because you have 21 14. But this one also is 14,. So that has the same amount of genetic material. Then you have this option where you get 21 right normally. But then the 14 that's chosen is actually this one. Right? And so now you have two copies of this 21 chromosome and one copy of the 14. And this could happen with 14 to write 14 14, 21. It could happen either way. But I've shown it to you this way because this is what ends up causing the Down syndrome. Um Or what could happen is you could just get the 14 Or just the 21 And this is more rare because this means that something else has happened for you not to get 21, but it is possible. So these are the four Gammy possibility. So if you were to major or essentially fertilize, you have this one gammy coming together with this one, so you get two copies of 21 and two copies of 14. And this offspring is going to appear normal because they have the exact amount of genetic material that they should. Then you have this mating where you get 21 14 and you get this robert Sony in translocation of 14 and 21 what you get is you get 21 14 14, 21. And this because it has the same amount of information is normal, it also appears normal, but it's a carrier for that Down syndrome because it has this and this makes it a carrier. Now you can have this combination where you have 21 14 from this parent And you also get 21 14, 21 from this parent. And that means that you have three copies of the 21 and two of the 14. And that is down syndrome. Down syndrome, trisomy 21. So now you have three copies of 21 because of the Robert Sony in translocation. And this means that you inherited down syndrome from a parent that didn't have down syndrome. And then finally you have you have this rare case where you have 21 14 and then just 14 and um what you end up with 21 14 14 or 21 21 14. And either way you're missing part of the information. And this is non viable. And so the reason that you um so these are the four offspring and this is how this happened. I want to go back for a second and explain how this would happen. So remember that when. So during uh manoa sis, what's gonna happen is you have 21 you have your 14, 21 you have your 14. Now, these are going to replicate, right? And then they're each going to go to one Um Gammy. So in this case where you have the 21 and the 1421 goes to one gammy Then this means that you have an extra 14, that's left by itself. And that's how you get this gamut here. So it does happen. So I just wanted to make sure that was clear because I'm not sure I explained that, but well, but anyways, this is how robert Sony in translocation, robert Sony in trans location means that you have two long arms of two different chromosomes now attached to each other, which is here and that is how it can lead to inheritance of these tress. Omi's especially like Down syndrome. Now, familiar down syndrome is about 5% of all Down syndrome cases. So it's very rare, but it does exist right? 5% is a good big number for these types of cases. And so robert Sony and trans locations, you know, do happen in humans and do cause a disease is fairly commonly for how you would, how rare you would expect them to be. So that's robert Sony in translocation. With that, let's not move on.

Which of the following represents the chromosomal segregation into gametes after a reciprocal translocation caused by adjacent-1 segregation? N=Normal chromosome T = Tanslocated chromosome

• A. (N2 T1) and (N1 T2)
• B. (N1 T1) and (N2 T2)
• C. (T1 T2) and (N1 N2)

Which of the following ways reciprocal translocated chromosomes are sorted produces viable gametes?

• A. Adjacent-1 segregation
• B. Adjacent-2 segregation
• C. Alternative segregation

An individual heterozygous for a reciprocal translocation has the following chromosomes. Which chromosomes do the gametes receive after alternative segregation? 

A B • C D E F G                        J K • L M N O P 

A B • C D N O P                       J K • L M E F G 

• A. A B • C D E F G and J K • L M E F G
• B. A B • C D N O P and J K • L M E F G
• C. A B • C D N O P and J K • L M N O P

An individual heterozygous for a reciprocal translocation has the following chromosomes. Which chromosomes do the gametes receive after adjacent-1 segregation? 

A B • C D E F G                J K • L M N O P 

A B • C D N O P               J K • L M E F G 

• A. A B • C D E F G and J K • L M E F G
• B. A B • C D N O P and J K • L M E F G
• C. A B • C D N O P and A B • C D E F G

An individual heterozygous for a reciprocal translocation has the following chromosomes. Which chromosomes do the gametes receive after adjacent-2 segregation? 

A B • C D E F G             J K • L M N O P 

A B • C D N O P            J K • L M E F G 

• A. A B • C D E F G and J K • L M E F G
• B. A B • C D N O P and J K • L M E F G
• C. A B • C D N O P and A B • C D E F G

How many chromosomes does a person who is a carrier for familial down syndrome caused by a robertsonian translocation have?

• A. 45
• B. 46
• C. 47
• D. 48