by Jason Amores Sumpter
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In this video, we're going to introduce X and activation and so recall from our previous lesson videos that females actually have two X chromosomes in comparison to males that only have one X chromosome and a Y chromosome. And so because females have two X chromosomes, of course, that means that they're going to inherit double the number of X linked genes in comparison to males, which Onley inherit one set of those excellent genes. However, even though females have doubled the number of excellent genes in comparison to males, they do not have doubled the expression of those excellent genes in comparison to males. And the reason for that is because female cells will randomly turn off or inactivate one of their X chromosomes during early development. And so when this one X chromosome and females is turned off or inactivated, it will not be expressed. And that's why males and females still have relatively the same amount of expression of their X linked genes and this X and activation. This turning off of X chromosomes. Onley occurs in female sells. It does not occur in male cells. Now the bar body is really just the scientific term that is referring to that highly condensed, inactive X chromosome that is found in female cells. And it turns out that this random ex and activation that occurs in female cells can result in a female expressing different A leal's oven Excellent gene in different cells because those two X chromosomes that Aaron female cells may have different A Leal's. And so, depending on which X chromosome is inactivated, there could be different expression in different cells. And so a classic example of X inactivation are these calico cats, which have color patches due to X inactivation, and so notice down below. Here, what we're showing you is a calico cat, which you'll notice has these color patches. Specifically, it has white color patches, orange color patches and black color patches, and it's for and so taking a look at the black color Patch region. Uh, the reason that it expresses this black color patches because early on in the embryonic development of this cat, one of its two X chromosomes is going to be inactivated. And so these two reds, uh, structures that you see here represent the two X chromosomes in this female calico cat. And so the two X chromosomes here, one of them is going to be randomly inactivated. And so if one of these x chromosomes contains on alil or a gene that controls the fair color on basically this khalil here is the illegal that represents black for um, if it is expressed, then the cat will have black for and if the other X chromosome has an alil that says orange for instead of black. For if this is the one that's actually inactivated, then it will not express orange for in that region. And so in the regions of the cat that have black for what happens is the X chromosome with the black Alil version is going to be expressed. Whereas the X chromosome with the orange Alil version is going to be inactive and it will not be expressed, it will become a bar body. And so the black version again is going to be active here, and that leads to black for in the calico Cat. And that reached, however, if we were to take a look at one of the orange patches on this cat and look at the cells with them within them, what we would notice is that it's the chromosome, the X chromosome with the black alil black for a little that is actually inactive. And so the black version here will be inactive and become the bar body, whereas the X chromosome with the orange olio orange for Leo is actually going to be active. And so in the regions where the cat has orange for its the orange alil that is active on that X chromosome and in the regions of the cat that have black for it's the black, uh, X chromosome or the chromosome X chromosome with the black alil that will be active. And so you can see here how this X and activation this random turning off or inactivation of one of the X chromosomes and female cells can lead to a different expression of different uh, Leal's. And so this here concludes our introduction to X inactivation, and 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