 I want to spend some time looking at the homologous chromosomes and I'm starting us here because these are the chromosomes we're going to draw. Remember, there are 23 pairs of homologous chromosomes in each one of your cells so we're simplifying this dramatically in order to be able to visualize and draw what homologous chromosomes are and we're gonna get a little more detailed here. I know that I've already said the words to you in the past. I think in the DNA lectures I think we talked about genes and forms of genes but now we're gonna layer that onto these homologous chromosomes and figure out how this even relates to genetic diversity. I'm gonna draw my homologous chromosomes as if they have gone through S. But if you look at this, if you look at our little scenario, our little situation here, we've got homologous chromosomes before and after S. We can either draw them as one little log or we can draw them as an X, a log X, an X log. I kind of feel like maybe we'll end up drawing them both ways. Maybe we will because that way it makes it a little bit easier because I don't have to draw the X logs but the X logs are gonna have the exact same thing going on here. I drew a homologous pair. They're not identical to each other in my drawings because I'm not a very good iPad drawer but it's good enough to illustrate that these homologous chromosomes are the same. Now I'm just gonna draw another pair of homologous chromosomes just so you see that okay they you can definitely tell now that these guys are homologs and these guys are homologs. Homologs. Remember one of them came from your egg parent and one of them came from your sperm parent. That's and that's inside you. That's inside your cells. So let's make a note of that. This is inside you and so my colors that I'm showing you are let's just say green from sperm parent and red from egg parent. That means that this little green guy came from sperm and this little red guy came from egg. There's so many ways we could illustrate our chromosomes. They don't actually come in colors. You can't actually tell which one came from your sperm parent and which one came from your egg parent but if you look at your egg parents DNA you have one of their chromosomes. One copy of each one of your chromosomes came from your egg parent and the other copy came from your sperm parent. Now this is the weird part because we're gonna draw these out. We're keeping track of our egg parent, our egg parent and sperm parent when producing our own gametes that will make little humans out there who could make little humans out there who then got my sperm parent and my egg parents genetics. Okay. It's a little weird. Where does the diversity come from? Well we need more, we need more, we need more language. We're cool chromosomes are strings of DNA. We're cool that we wind them up around histone proteins to get these little logs. That's awesome. What we haven't talked about yet is that each of these chromosomes has genes on them. Okay, we have talked about that. DNA, a strand of DNA that codes for a protein that does a thing is a gene. I'm illustrating genes for you in purple. Homologous chromosomes have the same genes. Did you hear that and do you love me? If this purple gene I just drew I'm gonna just call it the A gene. I don't even know if I want to do that yet. I'm gonna call it the A gene. I did that on purpose. That gene can have different forms but that gene does the same thing in both chromosomes. So if we were to say, okay the A gene, okay that's specific. That's the name of the gene. That's not a random gene. It is the A gene. The A gene causes I don't know eye color. Eye color is the trait that we're looking at. Okay and the A gene codes for the proteins that impact eye color, the trait. Do you have different forms? Do you think you have different forms of the eye color gene? Yes, you can have big A or little A. These are alleles. I'm gonna put it in a different color. These are alleles of a gene and again I know that I've talked to you about this. I know we've named the word allele and said it is a form of a gene because you can have blue-eyed alleles and brown-eyed alleles. So you can have different forms of the gene that codes for a trait. Please, it is about a million times more complicated. Heredity in humans is absurd. It's absurdly complicated and traits are not coded for by one gene and we're going to spend three lectures talking about heredity and how this happens but we need these words in order to understand why meiosis matters. Why go through all these weird processes because it's about genetic diversity. Okay, I'm gonna draw because I love you. I'm gonna draw one more gene. I'm gonna draw a gene on the little guys and we're gonna call this the B gene. We'll have a big B and a little B and we could say the B gene codes for hair color. The A gene codes for eye color. The B gene codes for hair color. The B gene has different alleles. You can see that the egg and the sperm have different alleles. What does sister chromatids look like? If we were like, okay you think you're all cool. What does it look like if we add a sister into the mix? It's easy. Sisters are identical. Sisters have the same genes. Sisters have identical alleles. Yes, that means that your sister chromatids are identical to each other. Homologous chromosomes, same genes. So what do you call that? I mean that they're the same but different alleles but different. All right, homologous chromosomes are wild. Keep track of them because we're gonna go through meiosis one. Two, just two stages of meiosis one. We're gonna look at prophase one and we're gonna look at metaphase one because that's where the big things happen. That's where the big differences take place and everything else, glory days, is just like mitosis.