 I have a picture of a cell here for you. This is my little golden cell. And you'll notice that inside my golden cell is a little light yellow nucleus with little blue chromosomes hanging out inside of that. This to me, I look at this and I'm like, oh yeah, that's the nucleus. That's what chromosomes look like. But a chromosome is nothing more than a little package of DNA. And I think that's really important to remember that the whole thing, otherwise you're like, dude, why are we doing this and why do we care? We care because we spent three lectures talking about the structure and function of DNA. So hopefully this right here looks totally familiar to you. But we also care because that DNA provides the instructions for making you who you are and your babies, who they are. Oh, those cute little parasites. So we'll talk about the structure of a chromosome in a second, but let's just look a little bit bigger picture. Inside, we've already said this, inside the nucleus of a human being we have 46 chromosomes. So I'm just going to make a list here. And inside, I better stay in the screen. Or that could be a really interesting lecture right there, dude, I better focus. 46 chromosomes inside the nucleus and the bottom line is that one chromosome equals one molecule of DNA. Okay, really, true story. I'm going to show you something because this is really cool. This is a yarn, whatever. What is this? A skein of yarn. And this yarn log is basically, do you agree, you could unravel the whole thing. This is a piece of DNA. In fact, you could even look at this little thing. You know how when you look at yarn, it looks like it's a little helix twirly thing? So imagine that this is my double helix strand of DNA. And if I bundle it all up, I've got this nice little chromosome. If I don't bundle it all up, then I actually can have the exact same thing, pardon me, while I get my, really, dude. Okay, you're going to have to pretend like the green piece is in here. Hold on a second, I've got more toys. Look, I've got a green one too. I've got a green one and a red one. These are my chromosomes. These are my logs of DNA that are, can date, there's 46 of them, inside the nucleus. And I could unravel them, right? And if I unraveled them, I would have like this tangled mess of yarn mess. My kids actually unraveled these and they thought that their life could not get better. They had so, like, isn't that kind of a dream to just go around and make a huge mess of yarn? That's what they got to do when they made my chromatin for me. This is DNA in the form of chromatin. It is, I could unravel this entire red string and wind it back up and get this. Do you agree with that? Does anybody want to try it? Yeah, no, not me. And my kids totally refused. They were like, no, we're not winding that back up. Come on, boys. Hustle. Get it wound. It's not happening. So that's cool because why would we have DNA in two different forms? We can have chromatin, which is just a tangle. Or we can have, we call it a chromosome, but I'm just going to call it a log. And a chromosome, when it is a log, it actually, it's not just a DNA log. It actually winds around these little protein beads. So if I was really a rock star, I'm only halfway a rock star. If I was really a rock star, I would take this and I would string some beads on there and then I'd wind it back up into this format with all the beads on there. And those beads are called histone proteins. So we get A plus histone proteins. And histone proteins are important. We're going to see them again when we start looking at biodiversity and we'll see that not all critters have histone proteins, but a lot of us do. And so we can actually tell who's related to who based on the presence or absence of histone proteins in the nucleus or in with the DNA. Okay, I want to show you a picture of chromatin. So yeah, you get this. Look at here are my little beads. Those are histone proteins. And the DNA, literally, the DNA is the blue line right here and it winds around those proteins and it helps keep it organized. Now think about this. Why? I'm going to show you a picture of chromatin. That's actually chromatin, remember the tangle. It's a chromatin inside a nucleus. And it looks like a tangle. Like that is so crazy cool. I love that. You can see that it is just a yarn that's all spread out in a crazy, it looks like a maze. Like wouldn't it be fun to go through and like walk through that? Walk through the DNA maze. Oh my gosh. Okay, settle down because it's really exciting. But now we want to think about why. Why do we have our DNA in two different forms? So I'm going to leave that for you to think about. And think about, okay, there's going to be two tasks that we have to carry out. Number one, if we're going to make two identical cells at the end of this whole process, we better have two complete sets of DNA. So we're going to have to go through DNA replication. And you tell me, which is going to be easier to replicate? I'll let you think about that. Number one, we're going to have to divide. We're going to have to, once we've replicated, oh, I'm blurry, come back. Hello. Once we've replicated our DNA, and we have two identical copies of the DNA because we've gone through DNA replication, which you know that whole process, then we're going to have to divide it equally between two different cells. So tell me, do you want to divide two logs? Or do you want to try to find the two identical green pieces of chromosome yarn inside this tangle? It's not even an issue for me. You don't even have to ask twice. I know exactly what I would want to do. All right, chromosomes are amazing and there are lots and lots of new words that we have to learn to describe our chromosomes. So we're going to talk about chromosome anatomy next.