 Hi, you guys. So we are starting today with, we're starting our exploration of basically how we reproduce and make babies, which is a really interesting topic. And we're going to start out looking at basically the human life cycle. And then we're going to dive into different processes that are involved in the human life cycle. So go ahead and push pause right now and you draw. Like what is the human life cycle? And we're keeping this very human centric, but know that the processes that we're going to describe in this session will definitely apply to other critters. And this section will set the tone for the next section where we talk about evolution and biological diversity, which is really cool. Oh my gosh, this whole course. Aren't you excited you're here? Because what fun? The human life cycle. Push pause, draw it out. What do you think? And now that you're back after having a hypothesis of what I'm talking about when I say the human life cycle, I'm going to do it for you. So let's look at this. If we break down, I mean, it's, yeah, one human critter. And actually, we need two human critters to make this happen. But think back on your cute little self. What were you in the very beginning? You were not an egg. I mean, you were not carried in by a stork. Half of you was an egg. Do you agree with that? Okay, I can't help it. Here's the egg. That's half of you. And just for the heck of it, we'll throw, you know, an egg isn't going to turn into you unless we have a sperm. Of course, but of course. And then we have to have, you know, aww, they combine. And then what do they get? What is it? This is actually a word that is something that we're going to have to know. We should be comfortable with. The egg plus the sperm, dude, I'm picking colors over here and this is really fun. The egg and the sperm. How many cells is the thing that results when an egg is fertilized by a sperm? It's one cell big. You started out as one cell. And I'm going to tell you right now what that cell is called. It's a zygote. Any fertilized egg is a zygote. Now hopefully you're thinking, okay, these are single cells. We know a lot about cells. We know they have nuclei. We just did this whole thing on DNA inside the nuclei. So we know that that's important because we got to have protein synthesis. So we're actually going to have to keep track of our DNA and the chromosomes inside our nuclei. The zygote here, literally, you have an egg that had half the DNA and a sperm that had the other half. And now you have the zygote, which is a diploid critter. It has, I'm going to write the word down because I believe, I mean, we're going to see this. It means that it has two copies of every chromosome. We'll see it again. But then this little zygote, what does it do? Dogs of a feather. It turns into this little grown person. I'm showing you that it's a grown up because it's wearing a top hat because do you know any kids that wear top hats? Not so much. And then now that it's a grown up with a top hat on, what's it going to do? It's going to make its own sperm or eggs because it has similar top hats too. And it can combine its sperm or eggs with someone else and make a brand new human zygote that's going to grow into a grown up now. Awesome. Pretty straightforward. There are two processes that are illustrated here that we don't know about yet. One of them is the process of mitosis. And that's what we're talking about today. Mitosis happens when a single cell divides a nucleus, divides, and makes an identical copy of itself. And that's how you end up with whatever trillion number of cells that are in your body. Another process happens. A different process happens to produce sperm or eggs. And that's meiosis. So meiosis is a process that happens only in your gametes. It only happens in a sexually mature organism. And I told you that my zygote was diploid. It has two copies of every chromosome. Well, my gametes, that's what these are. These guys are called gametes. And these are haploid. And if you think about that, I mean, we're going to go into a lot of detail on this. But if you think about an egg, that I'm going to give you my numbers because why not? Here we are. An egg, any human, has 23 chromosomes. And the sperm has 23 chromosomes. So how many chromosomes are in the zygote? Dogs? 46. And 46 chromosomes means we have two of each chromosome. Here we only have one of each chromosome. So if you didn't have a haploid cell to combine with another haploid cell, you might as well just go through mitosis and just butt off another cell that goes through mitosis and makes a new Wendy Riggs. That'd be awesome. That's cloning. Some critters do it asexual reproduction, but for some reason, most of us reproduce sexually. And in order to do that, we have to combine genes with someone else. And in order to make sure that we don't end up with two times as much DNA in our nuclei, we have to have a whole nother process to divide and to create the nuclei in our gametes. And that's meiosis. Okay. Today, we're talking about mitosis. Tomorrow, we're talking about meiosis. They're similar processes. They're a lot of similar things. If you don't, buckle down and understand mitosis first. Meiosis is going to blow your mind and make you sad. Don't be sad. Understand mitosis. And that's what we're doing today. We're going to start by looking at the nucleus itself. And we've been here. We've looked at the nucleus before. We've looked at our DNA inside the nucleus. But now we need to really look at, okay, what's in there? And how do we know? Shall we? Let's go to the nucleus.