A recurrent disadvantageous mutation will evolve to a calculable equilibrial frequency. This is a very simple concept, recognizing the importance of mutation in maintaining a supply of variation. Understand the mathematical expression of this concept. Be able to calculate the gene frequency at mutational equilibrium for a disadvantageous allele. Understand how mutational equilibrium can contribute to polymoprhism.
Selection can maintain a polymorphism when the heterozgote is fitter than either homozygote.
Sickle-cell anemia is a polymorphism with heterozygote advantage. Understand how selection coefficients against the homozygotes can be calculated, from data such as that presented in Table 5.9. 5.13. The fitness of a genotype may depend on its frequency. The modelling continues to grow complicated. Understand that frequency-dependent selection can maintain allele polymorphism.