 Hello everyone. Now that we've talked about the process of meiosis, it's time to discuss how this process incorporates genetic variation within a population. Genetic variation is incredibly important from an evolutionary perspective. If we didn't have it, everybody would look completely identical to one another. All the plants would look identical to one another, all the animals and so forth. And if you think about it, you want variation in your population because otherwise, if you have a disease that comes and wipes everybody out, they all have the same genetic makeup they probably wouldn't be able to fight it. There are three main processes that happen within or around meiosis that give genetic variation in a population. And I like to refer them as three different shuffles of a genetic deck. That's why we have our carts here. The first shuffle of our genetic deck deals with the process of crossing over. Now, when we go through the process of meiosis, remember that we discussed you can have chromosomes that come from your mom and come from your dad. In fact, half of your chromosomes will come from your mom and the other half of your chromosomes will come from your dad. So in this case, let's say in our example that the solid chromosome came from mom and the dotted chromosome came from dad. We also mentioned that during prophase one of meiosis, we tend to get our homologous chromosomes pairing up. And when this happens, a lot of times they get very close to one another. So close in fact that they bump into one another and they form what is known as a chiasma. A lot of times when they form this chiasma, they'll actually exchange arms of the chromosome. And so what you'll end up with is a chromosome that mostly comes from mom with a little bit of dad. Alternatively, you end up with a chromosome that's mostly dad but ends up with a little bit of mom. These will be carried through the process of meiosis, remember, and they shall form four different daughter cells. Of these daughter cells, one of them will have the part of the chromosome that's totally like mom. Another one will have a part that's got a little bit of dad. Another one will have the part that's a little bit of mom but mostly dad. And then the other one will contain the information that's all dad. Now keep in mind, in humans we have 23 pairs of chromosomes. So there's a really good chance that our sets of chromosomes are going to bump into one another and exchange genetic information somewhere within those 23 pairs. These will then go on to form the egg and the sperm. Some of them will look more like mom, some of them will look more like dad, and some of them will look like a complete mix. This is our first shuffle of the genetic deck. Let's talk about the second one. The second shuffle comes from a process called independent assortment. Now we talked about this earlier. This was one of Mendel's principles. Let's draw out an example where we have two sets of chromosomes. Again, from mom is going to be the solid and from dad is going to be the dotted. What Mendel discovered was that there was an equal probability that the chromosomes will line up either way. So you could have one cell where the chromosomes line up this way and you have all of mom on one side and all of dad on the other. But the other possibility is that you have mom chromosome here and a dad chromosome down below and vice versa. So when this goes to form the gametes in this particular situation you'll have all of dad and all of mom together. In this particular situation, which again it's a 50-50 chance, you'll have half mom and half dad. It's a mixture. Now again keep in mind this is a very simplified version and we're only talking about two chromosomes when in reality in humans we have 23 pairs. However you can begin to see if you combine this process with this process where you have chiasma formed and you get crossing over you can start to get a lot of genetic variation. The third shuffle of our genetic deck comes from the process of random fertilization. Random fertilization just means that any egg could pair with any sperm. So let's say this was a sperm cell and it could pair with any one of those cells which happens to form the egg. It's a completely random process. Keep in mind though that when eggs are formed only one is formed in the other three year polar bodies but any sperm could potentially fertilize that egg. Now we mentioned that from an evolutionary perspective you want to have genetic variation because otherwise everything would look the same and you would have nothing but a set of clones. There are advantages to this but realistically speaking variation is much better if in fact you have diseases come through because everybody has a different resistance to disease. Some of it's genetically based, some of it's based on exposure but also for the fact that if everybody was the same the best example of this would be the potato blight when farmers back in Ireland planted all of one type of crop. Most likely they were pretty genetically similar and they pretty much got wiped out by one particular disease. If they'd had multiple types of crops in there and a lot more genetic diversity they may not have had so many problems. Hopefully this begins to illustrate some of the benefits of genetic variation and at least how the process of variation happens. This is why when you have siblings even though you both have chromosomes from your mom and your dad you may look very different, you may act very different and sometimes it's a good thing.