00:01
The complex trait has a phenotypic value distributed according to a normal distribution.
00:07
So if i start by drawing a normal distribution, our trait, let's call it x, varies along this x -axis, and the probability of a particular organism having that value is given by the y -axis.
00:24
So this is a normal distribution.
00:25
Its mean, mu is 80, its standard deviation, sigma is 12.
00:31
Example of what this particular trait might be, it could be something like weight or height.
00:36
Those tend to be normally distributed.
00:38
The cent of the population has a value less than 104.
00:43
So 104 is above the mean.
00:47
So let's mark it on here.
00:49
And we want less than.
00:51
So we want this area to the left.
00:55
So how do we find it? well, we don't use raw values, but be normal distribution, we use z scores.
01:03
Z is equal to x minus mu over sigma.
01:07
So here we want 104 minus 80 over 12.
01:13
Okay, that is two.
01:15
This cutoff point is two standard deviations above the mean.
01:20
Now we want to turn this into probability or a proportion, and then after that we can turn it into a specific.
01:27
So the normal function is really complicated.
01:33
We don't do it by hand...