Hi in this video, we're gonna be talking about comparative genomics. So, comparative genomics is the study of genomics from an evolutionary um perspective. And so first let's understand how what are the terms of the different genes that are related between organisms? So first is we use the term home a log to define genes that have similar DNA sequences and usually some type of similar evolutionary origin. Now, Ortho logs are genes inherited from a common ancestor. And para logs are gene related by gene duplication. So if we look at what this looks like, we have some kind of early gene, there was a gene duplication that creates the alpha form and the beta form and then this evolves further into chicken, human and mouse, mouse human, chicken. So home a log is going to represent every version of this gene because it originally came from this early gene and therefore they're all going to have similar DNA sequences. Or the logs are going to be um jeans that are similar because they are driven from the same alpha gene, but they're actually found in different organisms. Para logs are going to be in the same organism. So these are both mouths. But these are two genes that arose for an original gene duplication, whereas the alpha gene is not a gene, right? It became the alpha and then evolved into Ortho logs in different organisms. Whereas para log underwent a gene duplication but it's found in the same organism. So that's kind of the first cell. Let's understand that terminology. Then you have file a ginny and file a genie is going to be the evolution history of a group of organisms? And so oftentimes evolutionary biologists are presented with some type of question. And that question is, how are these organisms related or how did this gene evolved between these different organisms? And they have to answer that question. And so to answer that question, they always apply two kinds of principles. The first is biological inference, and that is sort of inferring how genes came about. And to do that. They use a concept called parsimony and that is a principle that says to always choose the most simplest explanation. So the best example of this is we have mammals. So mammals don't lay eggs, right? They do not lay eggs, we know that, but there are certain mammals that do. And so platypuses, which is literally the plural of platypus, which bothers me for whatever reason. But anyways, platypuses are mammals that lay eggs. So how do they, how do they do that mammals don't lay eggs, but platypuses do. And so therefore platypuses have to contain genes that are important for egg development, including like egg yolks, they contain yolk genes and other mammals don't have them because they don't produce eggs. So the question here, the biological inference that they have to make is where do these yolk genes found in platypuses come from? And so there's two options here. Right. So what's the first option. Right. So that means that there was some kind of common Eggeling ancestor that produced all mammals and then eventually the other mammals just lost the yolk genes and platypuses contained them and remained having them. So that's one part. The second option, right, Is that there wasn't this common Eggeling ancestor. But instead these egg jeans and platypuses evolved independently of other egg laying organisms like birds, for instance, because platypus is not the only thing that lay eggs, multiple organisms on the earth. So here are your two options. So just using the using the parsimony, what what would you pick when you pick a or would you be which one is the most simple? Is it is it more simple that pretty much all these organisms laid eggs and then that evolves and platypuses kept that. But mammals eventually law lost it. Or is it that you have some organisms that evolved eggs and some that didn't. And then mammals evolved and these kept evolving eggs and mammals, most of them didn't. But then a couple of the mammals actually evolved eggs separately from these other organisms over here. I hope it's clear that a is the most simple that there was some kind of common Eggeling ancestor that birds evolved from that platypuses evolved from and that mammals also evolved from. But mammals eventually lost it. And so this is an example of how this type of genomics can sort of look at these evolutionary perspectives and figure out, you know how the genomes compare where these genes are coming from and how they're all evolving. So with that let's not move on.

Okay. So now let's talk about humans, mice and chimps and compare them. So human genomes they're a bunch of similarities with other organisms and you're probably already familiar with that. So first let's talk about mice and humans. So my mouse genomes very similar to human genomes. About 99% of human genes have some type of home a log and mice and they also have 90% Sydney. Which means that Sydney describes the order of genes. And so if you have gene a gene B gene C jeans E. Conserve Sydney across organisms. Mean that the mouse genes and the human genes have the same order. Even if they're not in the same place, it's just the conserved order of genes. So there's 90% of that between mice and humans which is huge. Um With chimpanzees it's even more similar. So chimpanzee genomes extraordinarily similar to humans. There's about 35 million single nucleotide differences between a human and a chimp. Um and if you compare this right, there's 35 million, it sounds a lot. But between just me and you there's three million. There's really not that big of a difference between me and you and me and a chimp. Um just about you know 10 times the nucleotide differences. Um But there is a major difference between chimpanzees and humans are is a major but it's minor compared to other organisms. But one big difference is um actually duplications of chromosomal segments um is a major difference that humans have more duplications than chimpanzees um in certain regions. So that's a big difference. But generally we know this humans very similar to other organisms because we all evolved from the same thing. So with that, let's not move on.