Boxplot of divergence between D. melanogaster and D. yakuba for genes that are significantly sex-biased in expression. The boxplots show the quartiles of the distribution of d_N/d_S, with a notch at the median value and whiskers extending to three times the interquartile distance. (M) Significantly male-biased; (F) significantly female-biased; (X) X-linked loci; (3L) loci on chromosome arm 3L.