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Current time:0:00Total duration:7:44

Video transcript

let's say there are two communities and orange community and a purple community and they're separate from each other and your job is to go into these communities and find out what the most common influenza type is that's circulating among the people so you do this and the first thing you discover is something that's pretty interesting which is that in the orange community turns out that they really only have influenza type A remember that there are three types of influenza and over here the only one that seems to be affecting people is type A so let me actually write that over here type A and if you go over to the purple community you actually find quite the opposite you find that over here people are also getting the flu but it's always because of type B so these people over here having influenza type B and influenza type B also has eight strands of RNA and let me write in purple then type B so that's what you learn in the first kind of day on the job now there are many different types of Type A that are affecting the orange community and what I have drawn for you is just the dominant strain the dominant strain so there may be a handful of Type A is affecting the orange people but this is the dominant strain and you know actually the same is true over here in the purple community they have a few different type B's circulating but the dominant strain is the one that I've drawn for you so now let me make a little bit of space and let me tell you what you're going to have to do over the course of the next year over the course of the next twelve months you're going to actually have to follow these two communities and what you're going to do is basically track out over that year what's happening with the dominant strain so that's what we care about not all the strains but just the dominant strain and you want to know how genetically different is it compared to what it was like on day one of your job so when I say genetic change I'm really comparing it to what it was like on the first day of your job comparing two initial initial strain so over the 12 months you'll get a real good idea of how much change happened while you're on the job so let's say you start out and you live close to the purple people so of course initially there's no change right you're you're doing the type B strain and you're saying well yep it hasn't changed yet but some time passes let's say you spend some time away and you come back and you visit the purple community and you ask them hey what is the common type B strain that you guys are seeing nowadays and they say well it's basically the same as it used to be hasn't really changed a lot but there are two point mutations that have happened so the dominant strain now has a couple of point mutations so it's a little bit different than it used to be and you say aha there is some genetic change happening here the dominant strain is changing a little bit and then you go and you kind of visit again sometime later and they say yep you know thanks for visiting again a couple more changes have happened since you last were here and you say ah interesting let's plot that a little bit higher so now the the virus the type B virus is looking slightly different from how it was when you first started the job and you keep going with this process and you know there's a mutation here another one over here some mutations kind of pile up and basically what you get is kind of a staggered line something like this where it kind of goes like that all the way to the end of the year so the end of the year comes and you look back at your virus and you say ah there are a few mutations you know it's a little different than what it was like when I started and those little mutations you can see with the yellow X's so what would we call this process we call it genetic drift this is genetic drift this is kind of the normal process that happens with many many types of viruses and bacteria really all viruses and bacteria make mistakes when they replicate and so you're going to see some degree of genetic drift over time so now here's the cool part you go to the orange community the Orange County if you want to call it that and you say hey I'm here to do the exact same thing with your type a influenza virus and well in the beginning of course it's not any different you come back a little bit later and you notice that this one has had a couple of changes a few mutations just like you saw before so you say okay well so far so good it looks like it's a little changed and then you find out that you know there's one more mutation and when you come back on another trip so you say okay looks like it's a little changed further and then a really interesting thing happens what you find out is on a third trip that this entire you know segment is gone and it's replaced by this so you see a huge new chunk of RNA so how do you plot that on your genetic change axis well it's really different isn't it so you'd say okay well gosh now that one-eighth of the you know entire thing is different that would be something like this that's a huge jump so you say okay well now there's been a huge genetic change and then you come back on another trip and you find out that there's a little mutation in this green RNA and maybe one over there so again you've got a little bit of change and you go and you find out that there was another mutation here maybe one over here and so you keep plotting you're you're very loyal to your job you keep plotting and then it turns out that there is another big shift let's say this piece gets changed out for this one and so again you have a big big jump right something like that and finally by the end of the year it kind of goes up again because you've got a couple more mutations so that let's say there's another mutation there and there so that's what it looks like right the genetic change over time for the orange one the type-a is actually looking quite different and this one actually has elements of what I would call genetic drift and shift and shift and more specifically this part would be kind of a big shift right this is where a whole chunk of RNA got kind of incorporated into the dominant virus these are two shifts that might have happened that year and these other parts let me circle the different color let's say over here this and this is actually looking more similar to what we talked about before these are just kind of steady changes steady mutations over time and this is kind of what we have come to know is genetic drift so with type a influenza done in orange you can see that there is some drift and some shift happening and with type b influenza there's only genetic drift now what happens and this is kind of the scary part about type a influenza is that whenever you have these giant shifts there are two here whenever you have these shifts the entire community hasn't really experienced that new type a influenza they're not used to it their immune systems don't know how to deal with it and so many many people can get sick and what we call it is a pandemic so in the past we've had a few pandemics and each time it's usually because of a big genetic shift that happens and many many people as I said get sick go to the hospital and can even die