Blackwell Publishing

Virtual Experiments

Directional selection Genetic drift Gene frequencies Mutational load Sex ratio Sexual reproduction

For a single genetic locus with two alleles, A and a - one dominant to the other - a simple equation can be used to calculate the change in gene frequencies between successive generations for different selection coefficients:

Δp = spq2 / (1 - sq2)

This Virtual Experiment reiterates this equation to simulate changes in gene frequency over 1000 generations for selection against the recessive gene a. Beginning with p =0.01, the experiment takes the selection coefficient, s, as an input parameter. Try running the simulation with different values for s. Which gene do you expect to increase? When would you expect the increase of this gene to be most rapid? Try to explain why the increase in the frequency of this gene slows down as it becomes more common.

Click to download the program. (PC)