Okay. So now let's talk about traditional versus the next generation of sequencing. Of course, from the time the sequencing of the genome became possible, there have been many different types and methods developed over the years that have improved upon this technology. So what your book calls traditional whole genome sequencing, or traditional WGS, requires the use of cells. And this is kind of the earlier method, right? It's traditional, so it's going to be the earlier way that the genome was sequenced. And so how this happens is you generate DNA fragments, like we said before. And how you actually sequence these is you put them into plasmids. Remember, plasmids are bacterial DNA. We give these plasmids a special name called vectors because we're putting the genetic information into them and then putting them into bacteria. And so they're vectors of this genetic material that we're putting in. So we generate the DNA fragments, we put them in vectors, these plasmids, and we actually put them into bacteria and grow up the bacteria, and that's how you get multiple copies of that small read, as the bacteria is replicating itself. It's replicating that DNA, and it's making multiple copies of the fragment that you put into it. So after you get enough bacteria, you have a ton of copies of this; you can actually take that DNA back out of the bacteria, sort of extract that DNA, and begin to read the sequence through the sequencing method, whatever sequencing method you want to use, shotgun sequencing, power of sequencing, whatever. And so you tally the reads, and then you use again computer software to overlap them, connect them, and in this case, we call them sequence contigs, and these are because they're contiguous sequences where the overlapped read is arranged into. So, that was exactly like the picture I showed in the previous video of all those different reads being overlapped.
The genome sequencing is very similar. Right? I mean, we went over the basic sequencing steps, but this one does not use cells. So you don't need cells to amplify that DNA. Instead, you use cell-free reactions, using various laboratory techniques, mainly PCR, if you're familiar with this. If you're not, don't worry about it, but if you are, PCR is a good way to amplify that DNA. And then you can use sequence software to sequence, and next-generation sequencing, whereas the traditional one you had to grow bacteria, and bacteria take up a lot of room. You have to grow a lot of it, and it's not very easy if you have 10,000,000,000 reads to grow 10,000,000,000 flasks of bacteria. But next-generation whole genome sequencing actually uses very small reaction volumes and it's generally automated through the use of a robot, and so you can actually do like billions of wells, potentially, through it.
So this is an example of traditional whole genome sequencing. You start with DNA, this is the genome, you extract it, you fragment it, you put it into these vectors, and remember vectors are circular, these are plasmids, they're circular bacterial DNA, and the green sequence here is the sequence you're interested in. You put them into bacteria, bacteria grow, they divide, they replicate, they create many different copies. You can isolate and extract it, then you sequence the vector itself, and then you have a bunch of fragments represented by these arrows, which you overlap and determine the actual sequence. So that is, sort of the two main types, traditional on the whole or the next gen. Traditional, it requires a lot more work, a lot more material, and growing in live cells, whereas next-gen is, mainly much more automated and can be done in a very small setting with small reaction volumes in a machine, without cells. So, with that, let's now move on.