Evolution of dominance in metabolic pathways

Area of Science:

• Evolutionary Biology
• Biochemistry
• Population Genetics

Background:

• Dominance is a key aspect of phenotypic robustness to mutations, influencing genotype-phenotype relationships.
• Previous explanations for dominance evolution faced challenges related to heterozygote frequencies and assumed metabolic constraints.
• The concept of inherent metabolic constraints suggested default wild-type dominance, questioning the need for evolutionary explanations.

Purpose of the Study:

• To challenge the assumption of default metabolic constraints in dominance evolution.
• To investigate the evolution of dominance in metabolic pathways by integrating enzyme kinetics and population genetics.
• To explore how nonlinear enzyme interactions and epistasis affect dominance modification.

Main Methods:

• Development of a theoretical model integrating enzyme kinetics (Michaelis-Menten) and population genetics.
• Analysis of a two-enzyme metabolic pathway model to study dominance modification.
• Generalization of findings to metabolic pathways with any number of enzymes.

Main Results:

• Wild-type dominance can be extensively modified in metabolic pathways, particularly with mutations decreasing enzyme concentrations.
• Dominance modification is achieved through alterations in enzyme concentrations or kinetic parameters (e.g., k(cat)), affecting saturation levels.
• Dominance evolves as a byproduct of selection, insensitive to heterozygote frequencies, especially with dual-effect modifier mutations.

Conclusions:

• The assumption of default metabolic constraints is questioned due to the exclusion of nonlinear enzyme interactions.
• Dominance evolution can occur in a frequency-insensitive manner, driven by selection for alleles with pleiotropic effects.
• Selection for dual-effect alleles offers a potential common mechanism for the evolution of phenotypic robustness to mutations.