Sex-Linked Inheritance

in this video, we're going to begin our lesson on sex linked inheritance and so recall from our previous lesson videos that the sex chromosomes include the X or the Y chromosome. And the sex chromosomes are gonna be the ones that actually determine the sex of the organism, whether the organism develops male reproductive systems or female reproductive systems. Now females are typically going to have two X chromosomes, whereas males, on the other hand, are going to typically have one X chromosome and one y chromosome. Now, sex linked genes are defined as genes that air found on either sex chromosome. So genes found on the X chromosome R X linked genes and genes found on the Y chromosome are. Why linked genes now? It's also important to note that the X chromosome is significantly larger than the Y chromosome, and we could tell just by comparing the number of genes on each chromosome. And so the X chromosome actually contained somewhere around 1100 X linked genes, which is a lot in comparison to the Y chromosome, which only contains about 100. Why linked genes and so again, just by comparing the number of genes you can see that the Y chromosome must be significantly smaller, since it has so many less genes than the X chromosome, which is gonna be significantly larger. And so, if we take a look at our image down below, over here on the left hand side, notice that we're focusing on sex linked genes and so you can see that here in red we are representing the X chromosome, which is significantly larger than the little Y chromosome that we have right next to it. And so the black band that you see right here represents an X linked gene because it represents a gene found on the X chromosome, whereas this band that you see over here on the Y chromosome represents a why linked gene now moving forward in our course were mainly gonna be focusing on the X linked genes and not so much on violent jeans. Now again, females tend to have two X chromosomes, as you can see here, and males, they tend tohave Onley, one X chromosome and one y chromosome. And so really, it's the presence of the why chromosome that's going to contain genes that allows for the male reproductive systems to develop now. What's also very important to note here in this video is that with each fertilization event, there's actually a 50% chance of having a female and a 50% chance of having a male. And so if we take a look at this pun it square that we have over here on the right hand side, which are notices that we're crossing a mother with a father. And again, females tend to have two X chromosomes, whereas males like the father tend have one X chromosome and one y chromosome. And so when my Asus occurs and these gametes are formed on, we complete the Pundits Square, which you'll notice is that in the offspring every time there's a 50% chance of having a female and a 50% chance of having a male. And so that is exactly what we're indicating here. A 50% chance of having a female with two X chromosomes right here and a 50% chance of having a male with one X and one y chromosome, as we see in these two possibilities. And so this year concludes our introduction to sex linked inheritance. But as we move forward in our course, we're going to continue to talk Mawr and Mawr about thes X linked genes and sex linked inheritance. So I'll see you all in our next video.

and this video, we're going to talk about X linked inheritance. And so it's important to note is that because females have two X chromosomes, they actually have to a leal's for each excellent gene where the females will inherit one alil from each of her parents. Now, because females have two a levels for each excellent jean, therefore, females can either be Homo zegas dominant or Homo zegas, recessive or the female could be hetero zegas. For the excellent genes. However, this is not the case for males because recall that males Onley have one X chromosome and a Y chromosome, but they only have one X chromosome, and therefore males only have one. Ah, Leo for each excellent Jean. Instead of having to a Leo's for each excellent gene like what females have and males, they're going to inherit one of their A leal's from their mother and zero of the illegals from their father. Because instead of inheriting an X chromosome from the father, they inherit a Y chromosome from the father, and so therefore, because males only have one a Leo. For each X linked gene, males cannot be Hamas, I guess dominant or recessive or Hetero Sica's. Instead, males are going to express whatever excellent Khalil is on their single X chromosome that they inherited from their mother. And so what's important to note is that down below in our example, really, all we're trying to say is that this experiment that we're showing you that tracks eye color and fruit flies is really what first revealed the X linked inheritance pattern that we're describing up above here in this text. And so it's important to note, is that there is. This image is tracking the eye color of these specific fruit flies. And then, really, there are two I colors that are possible. There are red eyes, and there are white eyes that are possible in this experiment. And so the gene for the eye color is found on the X chromosome, and so that means that this eye color gene is an X linked gene. And so there are two a leal's for this X linked eye color gene. The dominant Lille is going to be X r capital are, which would mean red eyes. And then the recess of Alil is going to be X lower case R, which would lead to wide eyes. And of course, the lower case R is recess if I've to the capital are which is dominant. And so when you took a look at each of these squares that we have down below, which will notice is that they represent different crosses. And so, in this first cross over here, what we have is a ho mose, I guess red eyed female, which is going to have to x capital ours. And we're crossing it with a wide eyed male and noticed that the white eyed male only has one X chromosome and whatever, uh, Khalil is on the X chromosome is what's going to be expressed. And so because it has an ex lower case R. This male has white eyes, and so when you complete the pundits squares just like how we complete the pundits squares of our from our previous lesson videos three only difference is that we need to keep in mind that the males are going to give, uh, their Y chromosome in 50% of the scenarios. And so what you end up getting is the X capital are here, is gonna be brought down on the same goes for this X capital R is gonna be brought down. And then, of course, the X lower case are here is gonna be brought across, uh, to both positions here and then over here the Y chromosome is what gets passed one. So again, 50% of the offspring are going to be males, and 50% of the offspring are going to be females. But of course, when we're breaking it down and looking at the females and the males independently of one another, what we'll see is that none of the females are going to have white eyes. So 0% of the females have white eyes, and over here with the males, 0% of the males have white eyes and the offspring. And so, of course, when you take a look at these other crosses, they cross a homo zegas, white eyed female with a red eyed male. And they get this particular result in the pundit square. And what you'll notice is with the females again, 0% of the females are gonna have white eyes, whereas 100% of the males are going toe, have white eyes and then down here in this cross they're crossing a hetero, zegas, red eyed female with a red eyed male. And what's important to note is this is the results that you get. And again. 0% of the females have wide eyes, whereas 50% of the males have white eyes. And in this last scenario here, crossing a hetero zegas, red eyed female with a white eyed male, you get 50% of the females having white eyes one out of two and 50% of the males having white eyes. And so, ultimately, what you can see is that this experiment showed that there is a difference in how males and females inherit this particular gene and these particular traits. And that's exactly what this scientists had noticed is that when he does these cross hey noticed that the males tend to have a different percentage than the females and many of the cases. And so this is part of the experiment that helped reveal thes excellent inheritance patterns, and one thing that's important to note that will touch more on later in our course is that when it comes to X linked disorders, males typically are the ones that are gonna be impacted or affected MAWR. And so what you'll notice is that on pretty much all of these scenarios, males are more likely to be affected. On DSO, Um, the females are either going to be equally likely is being affected or less likely of being affected. And that's again, something that will touch more on later in our course. But really again, the biggest take away of this image is that this experiment is what helped reveal the excellent inheritance patterns that we described up above here, in our text. And so we'll be able to get some practice applying these concepts as we move forward in our course, so I'll see you all in our next video.

in this video, we're going to talk about X linked recessive disorders as we talk about a specific example in hemophilia, inheritance. And so hemophilia is a disorder that's characterized by abnormal blood clotting. And it is an X linked recess ivo disorder found in humans now by X linked recessive disorder. Of course, the excellent part means that the disorder is associated with the X chromosome and a gene on the X chromosome and by recessive. What it means is that it's on Lee going to be expressive. The individual on Lee has the recess. Yvette Ah, Leo or the recess Ivo A. Leal's on the X chromosome, or X chromosomes. Now females must be home a zegas, recessive or have to recess if a leal's in order to be affected by an excellent recessive disorder, however, males, they only require one recess if I've alil in order to be affected, because they only have one X chromosome, and they only need to receive one recess of alil to be affected. And so because males only need one recess of a Leo that makes males much mawr likely that they're going to be affected by X linked recessive disorders. And so that is something that is characteristic of these X linked disorders that they tend to be mawr likely to affect males than females. And so, if we take a look at our image down below, notice that we're showing you a pundit square that is crossing a hetero zegas mother that is unaffected by hemophilia with an unaffected father that is again not going to be affected by hemophilia. And so the hetero Zegas mother is going to have a new X Capital H and an ex lower case H And again, it's the X lower case H that is going to be associated with the disorder. But ah, mother, that has an ex capital age. A female that has an ex capital age is going to be saved from having the disorder. And so the females need to have to explorer Case H is in order to be affected, whereas the males again on Lee need to have one explorer case h to be affected. And so when we complete this pundit square here, what we'll see is that we can bring down the ex, uh, capital H to these areas here so we can put the X here the X here and again, the Capital H And then we could do the same over here with this theme. X lower case H we could bring that down. So we will have the X and the X here on. They're going to have lower case H is. And then, of course, we can bring across the X capital H two here and over here. So we will have X and X here, and they'll both be capital h is. And then over here we're gonna bring across the why to this position into this position over here. And so we'll have the why here and the why over here. And so what you'll notice is that taking a look at the females the top half over here, uh, the females are going to be unaffected. And so you can see the reason the females are unaffected is because they have at least one capital H one X capital H. And when it comes to the males, which are gonna be down below right here, 50% of them are going to be unaffected. But 50% of the males will be affected. Uh or a least that's the likelihood of that. And so what you'll notice is that it's the males once again that are gonna be more likely to be affected by hemophilia, which again is characterized by abnormal blood clotting, the inability to form blood clots. And so this here concludes our introduction to X linked recessive disorders, specifically hemophilia inheritance. And we'll be able to get some practice applying these concepts as we move forward in our course on. So I'll see you all in our next video.

in this video, we're going to talk about the X linked recessive pedigrees and so excellent process of pedigrees are, of course, going to be pedigrees that depict an excellent recessive disorder and typically these excellent process of pedigrees. They show that mawr males are going to be affected than females. Also, females of an excellent recess of pedigree can Onley be affected if the father is affected and the mother is either affected or at least a carrier, or is at least hetero zegas for the disorder and all sons oven affected female will be affected when it comes to X linked process of disorders. And so if we take a look at our example down below, we can see a pedigree of an excellent recessive disorder. And so here we can label this as an excellent recess. It disorder, and really, it's looking at red green color blindness, and so red green colorblindness is an X linked recessive disorder. And so having an ex capital B means that it's going to be the normal vision that, uh, where the individual would not be color blind with this Khalil. But it's the X lower case B that is going to lead to having this particular color blindness. And so again, because it is an excellent recessive disorder, females are going to need to have two X lower case bees in order to be affected, whereas males Onley need one X lower case B to be affected. And again the affected individuals are the ones that are shaded here. So they're the ones that have the filled in black boxes, and which will notice is that all of the ones that have a filled in black box have X chromosomes. Onley have X chromosomes with, uh, the recess of Alil, and so notice that there is a large tendency for males to be effective. And so the vast majority of the people affected in this case are males. There's only one female that is effected here in this scenario, and that is a pattern that will help you identify X linked recessive disorders much more quickly. Just by looking at thio to see if mawr males are significantly affected than females. Now, notice again that a female can on Lee be affected if the father is affected and if the mother is at least a carrier. And so when we take a look at this female that is affected. She could only be affected if the father is affected and notice that the father is affected. And again the mother is a carrier, meaning that she is hetero zegas. And so that's the Onley way that a female can be affected. And of course, all of the sons of an affected female are going to be affected. And so notice that the Onley son of this couple is affected because the mother is affected. And so this year concludes our introduction to X linked recessive pedigrees. And once again, the biggest thing that you should be able to take from this is that Mawr males are going to be affected than females. And that is a big clue to help you identify excellent recessive pedigrees. So this here concludes this lesson and I'll see you all in our next video.

So here we have an example Problem that's asking, What is the inheritance pattern of the following pedigree? Over here, on the right hand side on. We've got these five potential answer options down below. Now, right off the bat, we know that we can probably eliminate Answer Option E. Since we didn't really talk a lot about why linked disorders, uh, in our previous lesson videos. Now next, one of the first things that you want to try to do to eliminate any of the X linked disorders, um, is to look at the distribution of the, um disorder across males and females. And so when you count up all of the individuals that are affected and not affected, which will realizes that there are five females that are affected and there are seven males that are affected and again the females are shaded circles, the affected females are the shaded circles, and the affected males are the shaded squares. And so there are five shaded circles and seven shaded squares, and so that's pretty close to each other. So because there's not a massive distribution here between males and females, then we might eliminate the X linked, uh patterns of inheritance. So that limits us to either an autism will dominant or an autism will recess of patterns of inheritance and recall that one of the key features of autism will dominant is that it is found in pretty much every generation. It tends to be found in every generation. And so when you look across generation one, you can see that it is certainly found. Here. You look across generation to and at first glance it does seem to be found in this generation. But which will realizes that this individual number seven here is not actually linked vertically to these parents. Which means that this individual seven is actually coming from another family. And so really, what we can see is that there has been a skip in the generation for the individuals that are connected vertically here. And so, Ah, skip in the generation is a symbol of, or a sign of autism will recessive. And it turns out that this is actually the case for this problem. And so what you can see is that the disorder is in generation one. It skips generation to, and then it's found in generation three and down below here. You can kind of see over here that it skips this entire side over here. This generation and the only reason that it may not have skipped over here is because there was an individual that was also affected that came into play. But again, this is how we can also determine that it is. Autism will recess now. Another way to check for this is we know that autism or recessive means that it's going to have, um, Thean Vivid Jewel's must be Hamas. I guess recessive in orderto have the disorder and so you could just put in some, uh, letters in here to figure this out. And of course, the individuals that are not affected must have at least one dominant khalil. So you could do that throughout, and then just see if this holds consistency throughout the entire thing, and you could perform pedigrees to check to ensure that it is actually possible for this pattern of inheritance to exist throughout this pedigree. But again, the easiest ways to just check for these clues, such as this skipping of a generation or the presence of the disorder in every generation. And so this year concludes this example, and we'll be able to get some more practice applying these concepts as we move forward in our course, So I'll see you all in our next video.