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Figure 1 | BMC Evolutionary Biology

Figure 1

From: Recombination rate and protein evolution in yeast

Figure 1

Substitution rate as a function of the effective strength of selection. The bold solid curve represents the slightly deleterious divergence rate between species. Remaining curves represent adaptive divergence under three scenarios: open triangles when the beneficial mutation rate (u b ) is 1% of the deleterious mutation rate (u d ); open circles when u b is 5% of u d ; 'X-marks' when u b is 10% of u d . The strength of selection against deleterious mutations (|N e s d |) is shown on the x-axis, where s d is the average strength of purifying selection. A. The average strength of positive selection (s b ) is equal to the average strength of purifying selection (s d ); B. s b is twice as strong as s d ; C. s d is twice as strong as s b . When selection is weak, mildly-deleterious substitutions outnumber adaptive substitutions; divergence in weakly-selected genes is therefore predicted to be negatively correlated with local recombination rate. As the strength of selection increases, adaptive substitutions predominate; divergence in strongly-selected genes is therefore predicted to be positively correlated with recombination rate. The adaptive divergence rate is u b (1 - e-4Nsp)/(1 - e-4Ns), where s is the average benefit conferred by each mutation, and p is the initial frequency of each mutation (results for p = 0.0001 are shown). The slightly deleterious rate is u d (1 - e-4Nsp)/(1 - e-4Ns), where u d is the deleterious mutation rate, and s is the average cost of each mutation (equations modified from [30]; N e = N). The assumption that the beneficial mutation rate is much smaller than the deleterious mutation rate is supported by theory and mutation accumulation experiments [38,55-57; but see 58,59].

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