Model of effectively neutral mutations in which selective constraint is incorporated

Area of Science:

• Population Genetics
• Molecular Evolution
• Theoretical Biology

Background:

• Selective neutrality is a key concept in evolutionary biology.
• Existing models often assume a constant fraction of neutral mutations.
• Understanding the impact of nearly neutral mutations is crucial for evolutionary rate studies.

Purpose of the Study:

• To propose a new model for neutral and nearly neutral mutations.
• To analyze the relationship between mutation rates, population size, and evolutionary rates.
• To compare the implications of nearly neutral versus advantageous mutations on evolutionary patterns.

Main Methods:

• Developed a model where selection coefficients follow a Gamma distribution.
• Defined effectively neutral mutation rate (v(e)) for specific selection coefficient ranges.
• Utilized the infinite sites model to derive formulas for heterozygosity and evolutionary rate.
• Analyzed the impact of parameter values (e.g., beta, s e) on heterozygosity and evolutionary rate (k(g), k(1)).

Main Results:

• Average heterozygosity increases more slowly with effective population size (N(e)) compared to models with a constant neutral fraction.
• Evolutionary rate per year (k(1)) can be constant across organisms if generation span is inversely proportional to the square root of N(e).
• The model predicts k(g) is approximately equal to v(e).

Conclusions:

• The proposed Gamma distribution model provides a more nuanced understanding of molecular evolution.
• Nearly neutral mutations, under specific conditions, can lead to constant evolutionary rates across diverse species.
• Slightly advantageous mutations, unlike nearly neutral ones, predict a strong dependence of evolutionary rate on population size, contradicting molecular data.