About natural selection that's your selections and mechanism right is how things happen and when we talk about Evolution we're talking about how things change but we're going to help populations change right individuals don't change they either survival don't survive but their population changes in terms of those in terms of those tracks sorry about a population donkey and host they're not producing fertile Springs so you wouldn't say donkeys and horses are a part of the same population and they're not able to to interbreed and you might hear this term gene pool thrown around a little bit in this unit too when we talk about a gene for what we're really talking about is all of the genetic information within that within that population so in terms of drawing some things that I'll get you to do mutation is the main way that you get variation if you get variety will come to that in a moment what I want you to remember and we got phenotype remember phenotype is the physical trait it's what you actually observe phenotype is the product of your genotype so your jeans don't forget it's also the a house or some sort of a building that's maybe over 200 years old it's been through the doorways and they're quite sure a lot of the old buildings in Tasmania from those convict times there's Stone buildings and all of the doors are only about this stuff it's not because they all had jeans for being really short what would be the reason that people will a lot shorter so remember natural selection acts on variation within that population so natural that it's populations that are actually changed in our problem all right so what I want to show you here you don't need to draw anything we've talked about mutations this year right mutation creates gen etic variation you get new combinations of of those nitrogenous bases and that can create different phenotypes we talked about sexual reproduction and how that creates the variation there's the crossing over of the of the chromosomes as the independence and then there's also the random fertilization of gametes we talked about natural selection and natural selection is predictable in the sense that you see patterns emerging individuals that are less it we would say they're less likely change depending on conditions. the 3 types of natural selection include directional selection, disruptive selection, and stabilizing selection. Genetic drift and a genetic drift is where you see a change in the population over time and when you compare the population in the past with the population of the presence and you can see that there are some big genetic differences here genetic drift is usually because of some sort of random events like a natural disaster. Increases the variation that you have in a particular population so let's say we've got two populations of bugs we've got a green population that's only made up of the green bugs we've got the brown population that's only made up of the brown bugs they're still the same species but they've been separated for some reason maybe they live on different Islands or other sides of a mountain range or something like that and what you have is gene flow is that you get new jeans added to that population it might literally be because we've got new individuals arriving into that population so the thing you just want to understand for this is that with gene flow it increases the genetic variation with the inner population so this circle on the left just now a lot more variety right now but what it actually doesn't decreases the variation between populations now this population is more like that one so sometimes it's good to have genetic variation to have gene flow.
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