00:01
When we need to look at evolution, there's many different things that can change the aleolic frequency of a population.
00:07
And i'm going to describe four of them for you.
00:10
So we're going to start with what's called the founder effect.
00:14
So with the founder effect, you basically have a main population and say this is the main island over here.
00:23
And then a few of them get separated into a different population.
00:30
And it can be because they migrated.
00:32
It can can be because there was, you know, maybe an earthquake and it separated two populations or two factions of the same population went to different feeding grounds and a river formed in between them, chasm, they couldn't get back, whatever.
00:49
There's a main population.
00:52
Some of them get isolated.
00:54
Founder effect.
00:57
When you have this, you now have two new allelic frequencies because because there's two populations.
01:09
And so that's a way that you can change that.
01:12
And they can even drift apart genetically from one another simply because their environments are different.
01:21
So you might over a long period of time have two distinct species or two subcategories of the same species.
01:29
But an example of this happening is darwin's finches.
01:36
He proposed that a lot of the finches.
01:39
Were so similar because there was a main population on the mainland, but then over time, some of them migrated to different little islands, and it created a new environment for those where different traits were selected for, and over time they just became more and more different because their environments were a bit different.
02:05
All right, another example is the bottleneck effect, and this is where you might have a whole population, but a lot of them don't survive.
02:16
Only a few of them do.
02:20
So say only this much survived, and all of these didn't.
02:27
So when you have a bottleneck effect like this, there are few survivors.
02:35
And those that do survive may have a different allelic frequency than the main population.
02:45
Like say, for example, in this picture that i've drawn, there's mostly white individuals, but in the population of survivors, it's like half white and half colored.
03:01
And so in this way, you can get a totally new frequency of alleles just because of the randomness of those who survive.
03:18
It might be simpler, but oftentimes with the problem that effect, it is not.
03:22
And, then this bottleneck effect is an example of a genetic drift where simply because of the ones who survive, the gene pool has shifted to one side or the other...