Okay. So, now let's talk about the steps of meiosis. Meiosis is completed in 2 parts, and luckily for us, each one of these parts is followed by either a 1 or 2, so we know what's going on. The first step is prophase 1, which occurs during meiosis 1, and there are 5 steps in prophase 1. Here they are, though I usually butcher the names, but there are 5 steps. Different things happen in each step. In the first one, the chromatin begins condensing. In the second one, a complex called the synaptonemal complex forms because the chromosomes are aligning and the homologs are actually coming together. We are often shown images of chromosomes that look perfectly lined up together, but normally in a cell, they are not condensed. They don't look like our typical representation of chromosomes. They're just kind of long strings that float around. They're not paired or anything. So in prophase 1, and especially in the zygonema stage of prophase 1, this is when they start pairing together and forming what's called the synaptonemal complex. Then, you have a third step. This is where crossing over occurs. Crossing over is an important part that we talked about a lot that happens with genetic recombination, and so crossing over happens in this step of meiosis. This will likely be a question, so know that crossing over happens here. And so what happens is that chiasmata form, and this is the structure that forms between chromosomes that are exchanging information through crossing over, and you can actually see these connections between the chromosomes at this point. Then you have the chromosomes. They're just staying here, and then in the very last step, the chromosomes begin to pull apart, but they can't really go because the chiasmata that helped in crossing over are still there, so it's keeping them together. And that's really important because if they pulled apart now, you wouldn't have proper meiosis. But because those chiasmata are keeping the chromosomes together, it's good news.

So here we have the beginning of meiosis, there has been DNA replication. You have a green and a green, so these are replicated. Red and red, replication has happened, And then you have these exchanges of materials here, where crossing over has occurred, and this occurs in this stage. So then we go to metaphase 1, so the chromosomes, or the tetrads now, right, because you have 4, because they've been replicated, are lining up at the metaphase plate, and the homologous chromosomes lie on either side. What happened is that we started off with homologous chromosomes. Right? Then they got replicated. Now when they got replicated, they're still homologous chromosomes. Right? So, if we were to label these chromosomes, it would look like this. So they have the same genes on them, they may have different alleles, but they're homologous chromosomes. So what happens is that when they line up in the middle, this is the middle. So the homologous chromosomes line up on either side of the metaphase plate, while the sister chromatids remain on the same side of the metaphase plate.

So here's the metaphase plate. These chromosomes go to this cell and these go to this cell. Now when that happens, you get one cell that has T T and one cell that has TT, and so these are haploid. Remember this. But that hasn't happened yet. We're still lined up in the middle, so then we have anaphase 1, the dyads begin to separate into one pole. This is called when the homologous chromosomes separate properly. Nondisjunction happens when the separation doesn't occur properly. So here's the metaphase plate, and we have 2 chromosomes here, and each one separates like this, that would be disjunction. But if we had chromosomes here, or like this, and these 3 separated this way, and this one separated that way, that would be nondisjunction, and it does happen. It causes a lot of different genetic disorders, so it definitely can happen. Now, separation is beginning in anaphase. Telophase, they're pretty much at opposite poles now, and the nuclear membrane is beginning to reform around them.

And then you have cytokinesis, which separates the cytoplasm and actually forms 2 cells. So here is what is pretty much a mix between anaphase and telophase, and you can see that the chromosomes have now separated to the opposite end of the pole, and cytokinesis is happening here, and we'll pinch these into 2 cells. So now we're starting with the 2 cells here, and we're on to meiosis 2. So what happens is you have prophase 2, and that lets us know we are in meiosis 2. This is really a short phase, pretty much the cells look like this here. Nothing super big happens here. It's usually very short, sometimes almost nonexistent. Then the chromosomes go to metaphase, so now the sister chromatids, like this, lined up on the metaphase plate. Right? Now, because this has gone into its own cell, so for mitosis 2, what happens is the sister chromatids line up on the metaphase plate. So this is meiosis 1, and this is meiosis 2, and this is the difference between the two.

So you can see here that now the sister chromatids are lined up in the middle. So what will happen is here's the metaphase plate. These two sister chromatids will go to this cell and these two sister chromatids will go to this cell, and the same happens for the other cell. These two chromatids go to this cell, these two chromatids go to this cell, go this way. So I don't have a great image for this, it's a little confusing. You can, if you compare the actual sister chromatids here, you'll see that they're separated, the colors are exactly the same. But essentially, anaphase 2, the sister chromatids begin separating, telophase 2, the chromosomes go to each pole, and then you have cytokinesis again, and this creates 4 haploid cells. So I've drawn 2 here, but there would be 4 with the same number of chromosomes in them, and you can say that, like I said before, these 2 sister chromatids go to 1 cell, so that would be this cell here. Whereas these 2 sister chromatids on this side of the metaphase plate go into this cell, and the same for the other cell as well. So these are haploid.

So to review, you start off with 2 homologous chromosomes. I'll write it like this, and I'll draw it like this. Oh, I want to use a different color. Hold on. So here we go. Then replication occurs, so then you get 2 copies. Right? Then you get meiosis 1. Right? And that creates 4 cells. So the metaphase plate is here or here. The division plate. So one cell gets this, one cell gets that, or this, this, however you like it. Then you have meiosis 2. These are haploid. Remember? Because you have one type of chromosome, even though you have 2 copies, it'd still be one type. So it's haploid, then you have meiosis 2, where you get 4 cells. So that would be big T, big T, little t, little t, or if you like the chromosomes drawn, 2 black and 2 red, which is also haploid because you either have black or red, not both together. These are diploid. So hopefully, you understand the difference between diploid and haploid and why this is how meiosis works. So, these are the steps of meiosis, so hopefully that makes sense. With that, let's now move on.