The theory of natural selection (part 1) - Can we predict the frequencies of genotypes?
An elementary population genetics model
Given genotype frequencies in generation n, an elementary population genetics model can be used to predict frequencies in generation n + 1. This model has four steps, starting with the frequencies of genotypes among the adults in generation n.
1. The first step is to specify how these genotypes combine to breed (called a mating rule).
2. The second step is to apply the Mendelian ratios for each type of mating;
3. We then add the frequencies of each genotype generated from each type of mating to find the total frequency of the genotypes among the offspring, at birth, in the next generation.
4. If the genotypes have different chances of survival from birth to adulthood, we multiply the frequency of each genotype at birth by its chance of survival to find the frequency among adults.
When the calculation at each stage has been completed, the population geneticist's question has been answered.
Figure: the general model of population genetics.