Linkage disequilibrium between rare mutations.

Area of Science:

• Population genetics
• Evolutionary biology
• Statistical genetics

Background:

• Linkage disequilibrium (LD) is crucial for understanding evolutionary forces.
• Theoretical understanding of LD, especially concerning mutations of varying ages and fitness costs, is limited.
• Existing models often struggle to capture complex LD patterns.

Purpose of the Study:

• To develop a forward-time framework for predicting linkage disequilibrium (LD) between neutral and deleterious mutations.
• To analyze how mutation age, fitness costs, and frequencies influence LD patterns.
• To provide a theoretical basis for interpreting empirical LD measurements.

Main Methods:

• Introduction of a novel forward-time simulation framework.
• Derivation of analytical expressions for frequency-weighted LD statistics.
• Analysis of LD dynamics in the limit of rare mutations.

Main Results:

• LD dynamics simplify significantly for rare mutations, allowing for heuristic interpretation based on lineage trajectories.
• Analytical expressions for LD statistics were derived, incorporating recombination rate, frequency scale, and fitness costs (additive and epistatic).
• Mutation frequency scale dramatically impacts LD curve shapes, reflecting diverse correlation time scales. Differences between neutral and deleterious mutations exhibit epistasis-like features.

Conclusions:

• The developed forward-time approach provides a powerful tool for predicting LD across various evolutionary scenarios.
• Results offer new insights into the interplay of mutation frequency, fitness costs, and recombination in shaping LD.
• The framework has direct implications for interpreting recent LD measurements in bacterial populations.