Models of Fluctuating Selection Between Generations: A Solution for the Theoretical Inconsistency

Area of Science:

• Population Genetics
• Molecular Evolution
• Evolutionary Biology

Background:

• Selection fluctuation between generations was a key topic in population genetics and molecular evolution during the 1970s.
• Previous studies suggested neutral mutations might fluctuate around a frequency of 0.5 due to fluctuating selection.
• This pattern was primarily derived from specific Wright-Fisher additive models, notably the Nei-Yokoyama puzzle.

Purpose of the Study:

• To re-examine the theoretical assumptions underlying fluctuating selection models.
• To identify the implicit assumption of a 'reference phenotype' in existing models.
• To propose a more comprehensive population genetics model accounting for different reference genotype possibilities.

Main Methods:

• Revisiting the theory of selection fluctuation between generations.
• Analyzing the constraint of constant fitness for at least one genotype (AA, AA', or A'A') in fluctuating selection models.
• Developing and analyzing a mixture model where each genotype has a probability of being the reference genotype.

Main Results:

• The emergence of balancing selection at a frequency of 0.5 is contingent on the heterozygote (AA') being the reference genotype.
• Existing models implicitly assume one genotype maintains constant fitness, which is not always explicit.
• The proposed mixture model demonstrates that balancing selection's occurrence is dependent on the relative proportions of the three possible reference genotypes.

Conclusions:

• The concept of a reference phenotype is crucial for understanding fluctuating selection models.
• A more robust population genetics model should incorporate the possibility of any genotype serving as the reference.
• The proposed mixture model provides a framework for analyzing how the proportions of reference genotypes influence balancing selection.