In the mouse, Mus musculus, survival in agricultural fields that are regularly sprayed with a herbicide is determined by the genotype for a detoxification enzyme encoded by a gene with two alleles, F and S. The relative fitness values for the genotypes are Genotype Relative fitness FF 0.72 FS 1.00 SS 0.45 Why will this pattern of natural selection result in a stable equilibrium of frequencies of F and S?

Key Concepts

Natural Selection

Natural selection is a fundamental mechanism of evolution where individuals with advantageous traits are more likely to survive and reproduce. In this context, the relative fitness values of the genotypes indicate how well each genotype performs in the presence of herbicide. The FS genotype has the highest fitness, suggesting it is favored in the environment, while FF and SS are less fit.

Genotype Frequency Equilibrium

Genotype frequency equilibrium refers to a stable state in a population where the frequencies of different genotypes remain constant over time. This occurs when the selective pressures balance out, allowing for a stable coexistence of alleles. In this case, the fitness values suggest that the FS genotype will increase, but the presence of FF and SS genotypes will prevent complete fixation of any one allele.

Balancing Selection

Balancing selection is a type of natural selection that maintains genetic diversity within a population. It occurs when multiple alleles confer some advantage, allowing them to coexist. In this scenario, the presence of both F and S alleles is maintained due to their varying fitness levels, leading to a stable equilibrium where neither allele completely dominates the population.