Expression divergence in pairs of paralogs of different ages. Expression similarity decays steadily over evolutionary time. (a) mRNA data and (b) proteomic data suggest similar trends. Proteomic data  are derived from relative antibody staining intensity examined either in tissue sections (tissue microarray (TMA), overall signal; tissue microarray focused (TMAf), focused signal in the staining cell subset) or through cell-line staining cell microarray (CMA). Figure 2a is a box-and-whisker plot, with thick black horizontal lines showing the median, a box drawn between the quartiles, dotted lines extending to the minimum and maximum and outliers illustrated as circles.