 So take a look at crossing over. Remember that I said that in crossing over homologs, literally swap pieces. And I have a little visual to help you imagine how this happens. First of all, do you agree that I have one homologous pair here? My green homolog and my red homolog. Do you agree that each pair, each individual homolog has a sister chromatid attached? So this is actually in prophase one of meiosis where my homologs have hooked up. I've also gone through and actually labeled three different genes here. And I can't remember if I've told you what an allele is, a form of a gene. I've tried it. I totally did that in the mitosis lecture. So I've indicated the different alleles with capital letters or lower case letters. That just means it's a different form of the same gene. So we could say, dude, this is the A gene and we've got big A and little A. Here's the B gene and we've got big B and little B. Totally random. The red chromosome could have a big B allele. Totally just switch this out and make a big B allele. I made them different just to mix things up a little bit. And so that you could visualize that these are all possible options. Crossing over means you have to swap one gene for one gene. So let's see how exactly I made this happen. Clearly I wanted to make sure that you knew that the sister chromatid is identical to each other. The green sister chromatids contain the same alleles. The red sister chromatids contain the same alleles. So now if we're going to cross this over, we're going to swap sections of DNA that contain the same genes, even though clearly these guys contain different alleles. Crossing over could totally happen with the green sister chromatids. But is that even like, sure, it might happen. It probably does happen. But is there any result? No, because you're swapping a big A for a big A. So who cares? You're not even going to know that you did crossing over. If you swap a big A for a little A, you're going to have some genetic diversity in the possible gametes that you're going to produce. Take a look. Done. Crossing over, cha-ching. We just crossed over. Now, if you go through metaphase, I mean, anaphase one and separate your homologues, and then anaphase two and separate your sisters, you can imagine that each one of these is a chromosome found in a gamete. And then you can see that one gamete has all big letters. The other one has a little A and a big B and a big C. The other one has a big A, a little B and a little C, and the other one has all three little C's. I mean, little letters. Do you agree that we just produced a diversity of different possible gametes? That's the process of crossing over. The next thing I'm going to show you is the process of independent assortment, which also results in increased genetic diversity from the process of meiosis.