X-Linked Inheritance

by Jason Amores Sumpter
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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.