Okay, so now let's talk about the f factor. So what is the f factor? Well, the f factor is what allows bacteria to swap DNA. It allows the bacteria to undergo conjugation. So if bacteria contain the f factor, we say that they are f+ and that allows them to donate genetic material. While bacteria that don't have it, we say are f-, and they can only accept genetic material. So not every bacteria can, like, initiate that conjugation; only bacteria with the f factor can. So what is the f factor? It's a plasmid, so remember what a plasmid is. It's that circular DNA that exists outside of the main chromosome. It's not necessary for bacterial survival, but it does give it certain advantages. This f factor is a plasmid that allows bacteria to undergo conjugation, which is a huge advantage because that allows for more genetic diversity, which is always a good thing. Now the f factor can actually be given to an f- cell, through conjugation and as well as other DNA as well. Right? That's conjugation. But it's important to realize that it has different DNA than what it started with. It's sort of a mix now between the two bacteria. So we call it a recombinant, but this is a recombinant via conjugation and not genetic recombination. And you may say, "duh, of course. It's conjugation. It's donating this DNA. It's not undergoing crossing over. The bacterial chromosomes aren't lining up and doing anything. Why are you even telling me this?" Obviously, that's the case. Well, the reason I'm telling you this is because it's going to get confusing, on the next page, with something that's a derivative of the f factor. So, I really want to get the point across that it was the f+ factor as a plasmid, that it happens through conjugation and not genetic recombination. So if we scroll down and look at what this looks like, we have bacterial cell 1, this is a donor. Bacterial cell 2, this is a recipient. So if I were to label f+ f-, which one would be plus and which one would be minus? Right. The donor would be the f+ because it's donating. It has that f plasmid, and the recipient would be f- because it doesn't. And so, here's the f plasmid here. You can see that this allows the donor to create the structure called the pili, and that structure allows for the conjugation of the two bacterial cells. You can see that it fuses and is starting to go into the other cell. And at the end, you end up with two cells with the f+ plasmid, the f factor. Now you may ask, okay, well, if it donated that factor, how come it still has it? Right? Like, it gave it away, so shouldn't it be f- now? The reason it's not, the main reason that it's not, is that usually, these cells contain multiple copies of the f factor. So if it has 30 copies, right, and I didn't draw it here for space, but if it has 30 copies and it gives one away, it's still got 29. Right? It's still f+, so it's not just completely getting rid of it, it's just spreading that f factor around. The second way is more rare, and it actually occurs in the recipient cell. But this is, again, like I said, a rare form of what happens. Most of the time, what happens is that there are multiple copies and it gives one away. Now, here we get to a little bit of confusion because there's a second type of cell called the HFR or the high frequency of recombination bacteria. Now these bacteria have the f factor, but it is not a plasmid. So at some point in this bacterium it actually integrated into the main chromosome. So it lost the plasmid. It no longer has it as a plasmid, but instead, it has it as a linear gene found in the chromosome. So now it's in the main part of the DNA. It's actually a gene. It's linear. It's completely different from the f factor, but it has the same function. Right? The f factor allows that bacteria to donate DNA. So if it doesn't have a plasmid to donate, but it's in the bacterial chromosome, it still wants to donate DNA. But if it's in the chromosome, it can't just give a copy of it away. That's not how this works. Instead, what happens is it has to happen through genetic recombination. Remember, and this is why I was telling you how if it's a plasmid, it's going through conjugation. But if it's the HFR and it's actually incorporated into the chromosome, the f+ can't be given to the f- via conjugation, because it can't just give its chromosome away or else it'll die. It needs that chromosome for life. So, how it does this is it can still make recombinants. It can still make f+ cells, but it has to do so through recombination, instead of conjugation. So what this looks like, I'm not going to go through the whole picture, but you can see here that instead of having it in a plasmid form, which is a circular form, here's this bacterial chromosome. And you can see it's actually a linear gene here in blue, is the HFR, and it still allows it to have this pili. It still can initiate conjugation, but instead of just giving that whole chromosome over to the other cell, it actually just recombines and makes a bunch of recombinants. So it has a high frequency of recombination because it wants to donate that DNA. It has that f factor, but it can't. So the only thing it can do is create those recombinations. Whereas, if it's a plasmid and it's separate, then it can undergo this normal conjugation and actually give its plasmid away. But the HFRs are actually really useful, almost even more useful than the F+ bacteria, at least in terms of humans, because we can use this HFR bacteria to map bacterial chromosomes. Now remember, the HFR is a linear gene. It's found inside the bacterial chromosome. And so how you would do this is you take an HFR cell and an f- bacterial cell. So this has the f factor in the linear, and this doesn't. So the HFR will stimulate the bacterial fusion, the bacterial conjugation, and it will start to transfer some DNA into the other cell in forms of recombination. Now the origin is the area where the first gene transfers or the first recombination areas start transferring to the other cell. Now, at any point, you can stop conjugation, or humans can, and when they stop it, it's called interrupted mating. And literally, what they do is they take bacteria who are undergoing conjugation, and they put them in a blender, like, really, like gentle blender, and that stops all conjugation. Right? Because it cuts that conjugation bridge, that pili, apart. And so now it can't finish what it's doing. But it's already started it, but it can't finish. So what happens is you actually get some of the genes that were really close to this HFR, which is where it started, will have already recombined before you interrupted it. So let's say you allowed conjugation for 5 minutes and interrupted at 5 minutes, well, the genes that are really close to the HFR will have already recombined in that 5-minute time, and the genes that are far away won't have had time to recombine in that period. So you can actually use minutes from, like, your interrupted mating from the time of conjugation starting to determine how close the genes are to that HFR. So this is what this looks like in the center of the passage. Here you have the HFR, it has the pili; it can conjugate. You can see that, it's getting transferred. Its it's undergoing, it's allowing recombination between these two bacteria. So here's the origin, which is where that started, and it always starts with that HFR. And then the genes that are really close to that HFR, if you interrupt it very quickly, soon after conjugation, will have stopped. Right? Then you can map how close those genes are to the HFR based on minutes past interruption. So with that, let's now move on.
