So duplications are exactly what they sound like. It's where you have a chromosomal segment and it's doubled. There are many different types. There can be tandem duplication, where the duplicate region, the normal, the original region, and then the duplicate, are adjacent to each other. You have insertional duplication, where the region, the normal and the duplicated, are located somewhere else. They're not adjacent. They're far apart from each other in the genome. Then you have very large segmental duplications, which are very large, 10 to 50 kilobases and encompass very large sections. These are rarer than, and occur mainly in a few organisms, so these are the really main important ones to know.
Here is an example of a tandem duplication. You can see there's an extra copy of gene B, and it has occurred right next to each other; it's adjacent. Here's an insertional duplication, which again, there's a copy of gene B, but you can see that it's located elsewhere far apart from each other on the chromosome. Insertional duplication can actually occur on other chromosomes as well. Didn't draw that here, do it on the same, but it can occur on the same or other chromosomes.
Now, duplications are extremely important in evolution. One of the main examples of this is actually rDNA. What is rDNA? Well, rDNA creates our RNA, which, if you remember what our RNA does, it creates the ribosome. Right? Our ribosomal RNA, this is really important for the ribosome. Now there are so many ribosomes. Right? Like, in humans we have so many ribosomes in every single cell. There are so many of them that if there was just one copy of this rDNA gene, we would not be able to survive. Right? Like, we have to have so many copies of these rDNA genes in order to create enough ribosomes to support the protein synthesis that we need to live. So if the rDNA gene had never duplicated, we couldn't survive. And so the duplications that occur to this rDNA gene are super important for making sure that we have the ribosomes available to do the protein synthesis that keeps us alive. And, so this is a super important, duplication and evolution connection.
Another one is that duplication actually results in 3 copies of an allele. Right? So if you normally have these 2 alleles, let's say the dot and so these 2 are important. Right? And the organism will evolve however it's going to evolve, but essentially these genes need to stay functional. Right? Because if they're not functional, that could kill the organism or cause them weird mutation that has a weird phenotype that prevents it from living or growing or reproducing or whatever. So generally, these are pretty restricted on evolution. They have to stay fairly the same over time, and they're not as free to evolve. But if you have a duplication, say you copy this allele here, now you have 3 alleles. So you have the 2 that are required for life, and now you have this third that isn't required and therefore is free to change over time. So it can mutate all over the place and eventually right? Mutations are more likely to develop in this third allele, right, mutations are more likely to develop in this 3rd allele because it's not necessary, right? Even just a duplication, if it's not there, the organism is still going to survive, grow. But because it's there, it can mutate. And sometimes those mutations will be really beneficial and they'll keep mutating, keep mutating, and eventually become something completely different that's super useful for the organism. Doesn't happen every time, but it definitely can happen. So that's how duplications are really important for evolution. So with that, let's move on.
