 I just think it's the craziest thing ever. And I mean, you know this by now about me that I just get like blown away every time I do this. It's so wild. Okay, so let's watch the whole thing. We've watched it once. Let's watch it again. Interphase, no problem. Same as mitosis, it's exactly the same. G1, you can't tell a difference, but the chromosomes do not have sisters in G1, but you can find your homologs and practice, practice identifying homologs. The beginning of S, we have a certain amount of DNA. At the end of S, we've doubled it because in meiosis and mitosis, it's the same. We double our DNA in S. We peaked at those chromosomes, now we have sister chromatids. This is the significant thing that happens in both meiosis and mitosis. Sister chromatids are identical. Homologs are the same, but different. Interphase, getting ready to do some dividing. Now, why I have an empty slide, I'm really not entirely sure, but the events of Prophase I have unique qualities. First of all, the things you would expect happen. The DNA condenses into chromosome logs. The centrioles move to the poles, the nucleolus disappears, the nuclear envelope disappears. The different thing, loud and proud, yell it out, friends. The homologs hook up. Good job. And we're gonna do the little timeout to see what crossing over is. What have I shown you here? These are homologous chromosomes. Let's point to something. What are those things I'm pointing to? Those are sister chromatids. What are these things I'm pointing to? Those are genes. Every chromosome has genes, and sister chromatids have identical genes to each other. Homologs also have the same genes, but not necessarily the same alleles. Remember that sisters have identical alleles. If it's the A gene and the B gene, sister chromatids both have big A, and in this case, big B. But homologs can have different forms. I have to get a drink of water. I'm not stopping. I'm really close to finishing this, so I'm gonna finish. I just can't yell quite as loud. What? Okay, we had our, oh, what are we gonna call these things? Hold on, hold on, my mouse, there we go. What do we call those guys? Those are different forms of the same gene. Those are our alleles. Alleles are different forms. This sets the stage for crossing over, so we get to watch it. Before everybody has their own alleles, after crossing over, they swap. They literally swap chunks of DNA. Because we've color coded sperm parent and egg parent, we can track the crossing over when it occurs. We would not cross over a B allele for an A allele. That would not happen, because that's like crossing over a head for a leg, and you wouldn't wanna make that trade, because then you'd have two heads and no legs. Bad idea. Okay, crossing over happens in pro phase one. And ta-da, we just made it occur. Pro phase one continues, we jostle around, we're jostling and jostling. This is why they say pro metaphase exists, and I think they say pro metaphase exists for meiosis as well, but I ignored it and just did metaphase one. Homologs have lined up on the metaphase plate. Anaphase one, we split homologs. That's the event. Cytokinesis and telophase occur, and we now have two daughter cells that are haploid, because they only have one copy of each chromosome. Even though they have twice as much DNA, count your centromeres, that's how you know. Pro phase two is the same as mitosis, and all we're doing is lining up our sisters on the metaphase plate. Metaphase two, sisters are lined up. Anaphase two, sisters split. Telophase two, sisters are in their poles and cytokinesis, we split the cells. We now have four unique haploid daughter cells, because we went through the process twice. Let's do a summary. This is what we started with. So we started with our pairs of homologs. That was an original, it was a diploid cell that we started with. After meiosis one, we ended up with two haploid cells. Look at that. Convince yourself. Six chromosomes in the first diploid cell, only three in the two daughter cells. And then split again, and we end up with the four unique gametes. The thing that we could do is we could make a copy of this entire PowerPoint and do a different alignment during metaphase one. We could do, we could line them up differently and we would end up with different gametes. The other thing, I said there was nothing new in this summary, but I do wanna add one thing that I don't think I've said yet. When we talk about independent assortment and the eight million possible gametes resulting from independent assortment, that does not consider crossing over. So crossing over means that those eight million are actually not identical. They are likely very, very different. Okay, meiosis is amazing. Heredity is next. And then of course we have to talk about sex. So stay tuned for the lectures that are coming.