In this video, we're going to take a look at how the process of meiosis works and at how it forms gametes. Now, you might remember from our previous video that sexual reproduction requires gameamtes, which we sometimes call sex cells and include things like sperm cells and egg cells. The important thing about these gametes is that they only contain half the genetic material of a normal cell. So we can call them hloid cells. Then when two of these gametes combine, they'll end up forming a normal cell that can go on to grow into a new organism. And because that normal cell will have two sets of genetic information, one from each parent, we call them dloid cells. In order to make these gamts though, a cell needs to undergo meiosis, which is a few different steps that you need to know about. First though, let's just quickly recap chromosomes so there isn't any confusion. If we were to take a human and look inside the nucleus of any cell, we'd find these things called chromosomes, which contain genetic information. In fact, we have 23 different types of these chromosomes in almost every cell in our body. In this cell, we've only shown four to save space, but just imagine there'd be 23. And for each of these 23 types, there's actually two different copies. One set is from the father, shown here in blue, and one set is from the mother, shown here in red. We can call the ones from the mother maternal chromosomes, and the ones from the father paternal chromosomes. Because we have 23 different types of these chromosomes and two copies of each, each of our cells is going to have a total of 46 individual chromosomes. Getting back to meiosis, the first step is to replicate all of the cell's DNA by replicating all of these chromosomes. This doesn't form entirely new chromosomes as such. It just adds an extra arm to each of the chromosomes we already had so that they all become an X shape like this with one arm being the original chromosome and the other arm being the copy. Next, these two armed chromosomes all line up along the center of the cell in their pairs. So here we have chromosome one for mother and father, then chromosome 2 from each parent, then three and so on. Importantly though, which one is on the left and which one is on the right is completely random. So if we looked at two more cells undergoing meiosis from the same person, the chromosomes in the first one might look like this and the other one like this. It will always be pair one, pair two, pair three and so on. But the left to right order will be random and so it will be different each time. And this point is actually really important because it means that in the next stage when the chromosome pairs are pulled apart and the whole cell splits in two, the chromosomes are going to be randomly distributed with each half of the split cell getting a different combination of maternal and pnal chromosomes which means the DNA in each of those two cells is going to be different. So, so far we've doubled all of the DNA and undergone the first division. Next, we have the second division. And for this, the chromosomes all line up along the center of the cell again. But this time, it's the two arms of each chromosome that are pulled to opposite sides of the cell. And when the cell is ready, the cells then divide in half again, leaving us now with four cells. Now, one of the strange things to understand here is that even though a couple of these gametes might look the same, they're actually all genetically unique because during the process of meiosis, there are tiny changes to each of them. So, what we have overall is four genetically unique cells that we can call gameamtes. And remember, there are actually 23 chromosomes in each, not just the four that we've shown in our example. So in male animals, these would probably go on to develop into sperm cells, while in females, they develop into egg cells. Then if a sperm and egg fused during fertilization, they'd form a diploid cell that could divide by mitosis over and over again until it forms an embryo and then a fetus and then finally a fully grown organism. If you haven't heard yet, you can find all of our videos on our website, cognito.org. You'll also find questions, flashcards, exam style questions, and past papers. And we track all of your progress so that you always know what to study next. So, sign up for free by clicking here or browse our playlist here on YouTube.