Chromosomal Abnormalities and Molecular Genetics (Intro Psych Tutorial #39)
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Chromosomal Abnormalities and Molecular Genetics (Intro Psych Tutorial #39)


Hi, I’m Michael Corayer and this is Psych Exam Review. In the last video I talked about behavioral genetics. We saw how twin studies can be used to estimate the influence of genes on particular traits or behaviors but one of the things that I mentioned was that we can’t see the role of individual genes we’re just getting an estimate of the relative strength of genes compared to the environment. So in molecular genetics we’re going to look at specific gene interactions; the role of specific genes on particular traits, behaviors, or illnesses. So we’ll start by looking at some chromosomal abnormalities. We mentioned in a previous video that you have 23 pairs of chromosomes and you get half of each pair from your mom and half from your dad. But in getting these chromosome pairs errors can occur, you can end up with extra copies or you can be missing part of a chromosome. So these are the chromosomal abnormalities that we’ll talk about. And when we talk about all of your chromosomes we can refer to your karyotype. Your karyotype is the total number and the size and shape of all your chromosomes. So these would be some karyotype abnormalities. OK, the first of these is Down Syndrome and you’ve probably heard of this. Down syndrome is a chromosomal abnormality and it results in intellectual impairment and it also results in certain characteristic physical features. A flattened face with upward slanted eyes and some other physical characteristics. So why are these occurring? What happens in Down Syndrome is that you get extra copy of the 21st pair of your chromosome. Instead of having two halves to this 21st pair, you have three. This is referred to as trisomy, for three chromosomes. Instead of two halves you get three and this is the cause of Down Syndrome. Now at this point I want to point out that there’s a difference between these two words here. When we say that something is genetic versus when we say that it’s inherited. You might think these words mean the same thing but they don’t. Because we can say that Down syndrome is genetic; it occurs in the genes, it’s a genetic abnormality that causes Down syndrome. But Down syndrome isn’t really inherited. What I mean by that is, it’s not passed down from your parents. It’s not the case that your parents have this extra copy and they pass it on to you. So you don’t inherit Down syndrome from your parents even though it’s genetic. And you don’t pass Down syndrome on for the most part because most people who have Down syndrome are going to be sterile, they’re going to be incapable of having children. That’s true of males with Down syndrome and it’s true of about half of females with Down syndrome. They’re not able to have children so it’s not the case that Down syndrome is being passed on through generations. Each time Down syndrome occurs it’s usually a new mutation. It’s this mutation, this chromosomal abnormality that just happened to occur for that person. And it could happen at any time, it wasn’t the result of anything in the parents’ genes that caused the Down syndrome to occur. It’s not inherited even though it is genetic. OK let’s look at a couple other chromosomal abnormalities. Both of the next two examples are going to occur on the 23rd pair. And the 23rd pair is where you get the chromosomes that determine whether you’re male or whether you’re female. Now if you’re male then this pair looks like this: you have an X chromosome and a Y chromosome. If you’re female, you have two X chromosomes. So it’s this Y chromosome here that makes you male. And now when these two people here are going to have offspring, the mom can only give an X chromosome, either this one or this one, you get half from your mom, so she’s going to give you one of these. And the other half from your dad, so if your dad gives you his X chromosome, then you’re going to be female. If your dad gives you his Y chromosome, then you’re going to be male. Now if you think about this, this means that if you’re male that your Y chromosome, of course came from your dad and where did he get it? He got that same Y chromosome from his dad and he got it from his dad, and he got it from his dad. We can actually trace the Y chromosome through the male line. You can find your male ancestors just by that Y chromosome. That can tell you exactly who your dad was, he’s going to be the person with that same Y chromosome and his dad had it and his dad had it. Whereas for females, we can’t do this. We look at the X chromosome, we go back, we say let’s say it came from your mom here. Did this one come from her mom or her dad? It could be either. Did that come from her mom or her dad. We get lost. It can jump back and forth between coming from the male side or the female side. So for females if we want to trace the female line we can follow the mitochondria. This is kind of a sidebar here but the idea is that sperm cells don’t have mitochondria so you don’t get any mitochondria from your dad. But egg cells do have mitochondria so all of your mitochondria come from the egg, which obviously came from your mom and where did she get that? From her mom’s egg, so where did she get that, her mom’s egg, so you can trace the female line with mitochondria. But let’s get back to our chromosomal abnormalities. OK so you either get XY or XX to make you male or female. Or, you might have guessed, you get some other thing that might happen. You could end up with Turner syndrome. So what happens in Turner Syndrome? Well in Turner syndrome you get an X and then you don’t get the other half. It’s missing. So you’re XO. You only have one chromosome on this pair. So what happens? Well, you’re going to be female. Why are you going to be female? Well because we’re all female initially. Female is sort of the default state in terms of development. We start as female and then if we have a Y chromosome it turns us into males. So you don’t have a Y chromosome so you don’t get turned into male, so you’re going to be female. Unfortunately you’re going to also be sterile, so you won’t be able to have children. So again, this means this is genetic but it’s not inherited because it’s not getting passed on. You’re going to have some characteristic physical features as well. People with Turner syndrome tend to have a webbed neck, the skin on their neck is kind of webbed, they tend to have swollen feet, and they may or may not have some ambiguous genitalia. So they might have some sort of strange development of their genitals that don’t look exactly male or female somewhere in between. Ok, so that’s Turner syndrome. Now let’s look at another chromosomal abnormality on the 23rd pair and this is Klinefelter syndrome. In Klinefelter what happens is you have an XY, so you’re going to be male, there’s that Y chromosome making you male, but you also have an extra X. You have trisomy here, three chromosomes on this, what should be a pair. So what happens when you have Klinefelter syndrome? You’re going to be male, you’re likely to sterile some males with Klinefelter syndrome are able to produce sperm, but you’re probably going to be sterile if you have this, maybe not. But you’ll also have some other physical characteristics so you’re likely to develop breasts, you tend to be taller than average, and you tend to have smaller than average testicles. So that’s what happens in Klinefelter syndrome and you may also have ambiguous genital development, that can also happen in Klinefelter. Ok, before I move on I want to talk about one other thing. This is not a chromosomal abnormality but it’s related to this idea. We have these chromosomes but we don’t necessarily fully develop as totally male or female there are other possibilities that can occur. So I want to talk about AIS. The reason I want to talk about this is because it was in the news within the past week so you may have heard about it. AIS, this is Androgen Insensitivity Syndrome, and the reason you may have heard of it recently, is that there’s a Belgian model named Hanne Gaby Odiele and she recently came out and said that she’s intersex, meaning she’s not really male or female. She’s intersex because she has this Androgen Insensitivity Syndrome. So what does this mean? Well, if we look at her chromosomes, she’s male. She has XY as her chromosome. So why isn’t she really male? Well, she has a Y chromosome, but when it tries to turn her male from the default female state, she’s insensitive to androgen, her cells to respond to it. So the male hormones, the androgens, aren’t able to do their job, they’re not able to turn her into a male like they normally would for somebody who’s XY. So this means that even though she is chromosomally male, she’s going to appear female. She doesn’t have female sex organs, she has testes inside her body, I think actually she mentioned that she had them surgically removed, but she’s male in terms of chromosomes but female in terms of physical appearance and all this also shows how this process can be kind of complicated. It’s also possible, not just to have AIS but to have different degrees of AIS. So you could be completely androgen insensitive meaning you have no response to androgens. In that case your body is going to be sort of hyper-feminine. There’s going to be no masculinization of your body because it’s not responding to androgens at all and most females have some response to androgens. Females do have testosterone in their bodies, so that’s going to be a complete case of this. Or you could have a mild case or a partial case of androgen insensitivity. That means you have some response but not the full response that other males have. So you’re going to end up somewhere in between. This could affect your genital development, your physical appearance in some ways. The reason I bring this up is it shows that even when we have what appears initially to be this very clear distinction of we have male chromosomes, female chromosomes. It actually can get very complicated. We can have different chromosome pairings, we can have missing chromosomes and then we can have different response to what those chromosomes are trying to do and so it gets very complicated very quickly, even if we’re just trying to look at biology. That’s without even getting into socialization and cognition and other things that are going to relate to our sense of whether we’re male or female or something else. OK so I want to end with one more example of molecular genetics and this is a specific gene rather than talking about chromosomes here I want to end with an example of PKU. What is PKU? This is a disorder called phenylketonuria and what happens in PKU, this is a case where we have something that is genetic and it is inherited. So you get this because you inherit these genes, this particular gene from your parents. The way that it works is you get two copies of this gene. If you get one bad copy and one good copy then it’s OK, you’re fine. But if you get both versions from your mom and from your dad you get the bad copy of this gene then you end up with PKU. So what is PKU? Well, normally the good copy of this gene allows you to produce an enzyme. This is an enzyme called phenylalanine hydroxylase. PAH. OK so if you have the good version, the healthy version, you produce this phenylalanine hydroxylase, this phenylalanine hydroxylase is an enzyme that breaks down phenylalanine. So why do you want to break down phenylalanine? Well, phenylalanine is toxic. It’s bad for your neurons, it can hinder their development, it can damage them, it can cause intellectual impairment, it can cause seizures. So phenylalanine is bad, you don’t want it in your body. And the bad news is phenylalanine is in a lot of foods, meats and cheeses and things have phenylalanine in them, it’s an amino acid that occurs naturally in these foods. So if you have PKU, you don’t produce this enzyme. If you don’t have this enzyme then you don’t want phenylalanine in your body because you can’t break it down. so, if you do have phenylalanine in your body it’s going to accumulate and you’re going to have cognitive impairment, you’re eventually going to have seizures and other problems. OK so what’s the point of bringing this up? Well, here we have something that’s clearly genetic. But we can still see the role of environment. It turns out that if you have PKU and you detect it early before any damage has been done and we are able to detect this early, we can just avoid foods with phenylalanine and you can supplement your diet with some other amino acids and what happens is now you’re fine. You don’t develop the impairment, you don’t develop the seizures because you avoid the phenylalanine you don’t allow it to accumulate and therefore this thing that appeared to be purely genetic actually has this environmental component. Ok, so I hope this helped you to understand some of the complexity of some biology, hopefully this wasn’t too much at once, but we’ll come back and we’ll see other examples of chromosomal abnormalities, of genetic abnormalities, the role of specific individual genes on certain things. Essentially you’ll just see that it’s really complicated and even when things appear to be purely genetic, there’s often still an environmental component. That’s really an important thing to keep in mind. Your genes, for the most part, are not fate. Even in something like PKU. Ok, so I hope you found this helpful, if so please like the video and subscribe to the channel for more. Thanks for watching!

One thought on “Chromosomal Abnormalities and Molecular Genetics (Intro Psych Tutorial #39)

  1. "We're all female initially" No, we're not. If you get a Y and an X chromosome, you're male from the start. If you get two X chromosomes you're female from the start. Go to the human genome project website. I had high hopes for this video but with that statement, lost it all.

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