 So let's start out. Here is an image of a karyotype and I want to know from you what stage of the cell cycle do you think that this karyotype is collected during? Did you follow that? If when I squished this cell and like broke open its nucleus and poured out these chromosomes, what stage of the cell cycle could I possibly be in? Could I be in interface? No, of course not, because what is the form of DNA in interface? It's in the form of chromatin, so it's going to be your tangle. It's not going to look like this. So it has to be sometime post-prophase. Do you agree with that? Because if it's before prophase, it's condensing. And we want to get pictures of the chromosomes in their most condensed form. And that actually happens during metaphase. So this image came from a cell that was in metaphase of mitosis. Now, there's an activity and it's actually linked in canvas and it is from the biology project in the... well, it's got Arizona in its... I feel like there's something in Arizona, the University of Arizona, that's what I thought. They've got this really cool activity and it's linked in canvas, so you can go check it out. But basically, they are having you sort chromosomes to basically build your own karyotype. So look at this thing. This is what the pre-karyotype actually looks like. It is not sorted into a nice little pile like this. Once you do your job at the University of Arizona Biology Project site, you'll have a complete set of chromosomes that have been sorted and you have to look for things like we talked about this in some previous lecture, that the striping is significant. The location of the centromere is significant. The length of each foot of the chromosome is significant. So you can tell that we can lay them all out here. We know that this is from a diploid organism and we've got two copies of each chromosome. I just told you that these chromosomes were taken from a cell in metaphase of mitosis. Is there anything about this that makes you go, yeah, I'm going to call BS on that? Anything? Well, I don't know. For me, I looked at it and I was like, dude, I'm calling BS on this because I don't see sister chromatids. And if this is a cell in metaphase, there should be sister chromatids. Look, there are sister chromatids. They're just super squished together so you can't really see them. See, these actually are sister chromatids. This is just an image or an example of how, yeah, there are sister chromatids in this mess right here. There's a lot of information that you can get from a karyotype. For one thing, you can tell from your karyotype whether the individual donating those chromosomes is male or female. You do that not by looking at any of these chromosomes. Chromosomes one through 22, those are autosomes. I kind of want to write that down for you. I'm going to because that's important. So autosomes, there are 22 pairs of autosomes in the human genome or in each one of your diploid cells. And then there's one pair of what? Of sex chromosomes. And you have two possibilities. You have two options. There's an X chromosome and there's a Y chromosome. And everyone has an X chromosome. Everyone. And you, I guarantee, have at least one X chromosome. If you don't have at least one X chromosome, done deal. Sorry for your luck, man. You're not here. So I know you have at least one X chromosome. If you are a female human like a like a me, then you're going to have two X chromosomes. And if you're a boy, then you have the infamous Y chromosome. And you can actually look at our karyotype and tell, okay, give it to me straight. Do you think, do these two chromosomes, this is my XY zone. Do these chromosomes look the same? Does it look like two Xs or do they look different? Hopefully, you're like, dude, those are different. One's huge and massive and beautiful. One's like a little weenie, tiny thing. And in fact, no damage intended. An X chromosome is very large and the Y chromosome is tiny. It's one of the smallest chromosomes in the human genome. So if you've got a mix, it still is considered a homologue, even though those are clearly not even close to the same chromosome. So you can see that there's going to be some interesting consequences of this fact when we look at genes carried on the X chromosome. Of course, genes carried on the Y chromosome, the ladies will never have. Like if there is a disease on the Y chromosome, that will only affect male humans. If there's a condition on the X chromosome, you'll see that there are some interesting inheritance, what's the word, consequences for that. So the next thing we're going to look at are traits that are carried on these chromosomes, most likely the X chromosome, and we call that sex-linked inheritance.