Fig. 2.

Testing the null hypothesis of the same distribution of s in both species. The log-likelihood surface for the shape and scale parameters of a gamma-distributed DFE(s) for (A) humans, (B) Drosophila, and (C) both datasets combined (constrained model). Colors from yellow to red indicate the difference in log-likelihood of that set of parameter values compared with the MLE (see color scale). For example, orange indicates parameters ∼100 log-likelihood units below the MLE. Proportions of mutations for various ranges of |s| are computed from the estimated (D) gamma distribution, (E) mixture of gamma distribution with neutral point mass, and (F) log-normal distribution. The gray bars indicate the proportions under the null hypothesis of the same distribution of s in both species (constrained model). Darker colors in E reflect the estimated proportions of neutral mutations.