This tutorial introduces formal population genetic models. We first establish what the variables are that the models are concerned with, and the general structure of population genetic models. We look at the Hardy-Weinberg equilibrium, and see how to calculate whether a real population fits it. We then move on to models of natural selection, concentrating on the specific case of selection against a recessive homozygote. We apply the model to two examples: the peppered moth and resistance to pesticides.

Key Questions:

• Can we assess the frequencies of genes or genotypes?
• Can we predict the frequencies of genotypes?
• What is the proof of the Hardy-Weinberg ratio?
• Why is the Hardy-Weinberg ratio useful?
• How rapidly do populations change through time?
• Are there examples of rapid evolutionary change?
• Summary