Distribution of selective pressures by classification. Boxplots comparing the distributions of ω values according to different gene-classification schemes. A: The photoreceptor cell-type specificity of the encoded proteins. B: The specific process in which the encoded protein is primarily active. C: The specific function of the protein (note that here “enzyme” refers to the enzymes of the retinoid cycle).
Invergo et al. BMC Evolutionary Biology 2013 13:52 doi:10.1186/1471-2148-13-52