Hi, my name is Andy Clark, and I would like to tell you about the human population
growth and its impact on genetic variation.
We're going to begin with some simple
population genetics to get an idea
of what we expect to be the behavior
of genetic variation in a population of different sizes.
First we're going to start with a particular model called an infinite alleles model,
and this model describes the balance between the input of genetic variation
by mutation, and the loss of that variation by random genetic drift.
This model predicts that the amount of heterozygosity, H in the population
at equilibrium will be theta divided by theta plus one.
I'll spare you the derivation of that, but
this is an essential conclusion from this infinite alleles model.
Theta is the population mutation rate,
and theta is equal to four times the effective population size
times the mutation rate.
I'll be talking a little bit more about what that term "effective population size" is in just a moment.
As I mentioned, H is the heterozygosity of the population
or the probability that when you draw two copies of a gene,
they will be different from each other in a sample from that population.