We will now look how population size and allele frequency has an effect on how fast a population reaches fixation. In our Virtual Mosquito Lab we can observe three different populations simultaneously. You can choose the size of population and the initial allele frequency for each population individually. Press the "Evolve" button to start the simulation. The "Reset" button allows you to start again with 3 new populations. Use this simulation to carry out the following experiments:
Experiment 1: Effect of Population Size on Rate of Fixation
The rate of fixation is a measure of how quickly an allele becomes fixed in a population.For each of the 3 populations set the same initial allele frequency (e.g. 0.5) but use different population sizes.
- Q. Does the size of a population affect the rate of fixation?
Experiment 2: Effect of Initial Allele Frequency on Rate of Fixation
This time keep the population sizes constant and vary the allele frequencies.
- Q. Does the initial allele frequency affect the rate of fixation? How?
Experiment 3: Rate of Fixation of New Alleles
We saw in the first section how new alleles are created by mutations in the germ line. When a new allele is created this way it only happens in a single individual in the population, therefore it is at a very low frequency. We can simulate this by setting the appropriate allele frequency, try to calculate this for each population size.
- Q. Do many new alleles persist in the population for a long time?
- Q. Do you think that a new allele has a better chance of surviving in a small or large population?