Female-biased expression of pairs of coding and non-coding X-linked genes is validated by quantitative RT-PCR. The RNA expression of co-localized pairs of coding and non-coding genes in three tissues, normalized to Actb and Gapdh is shown. Brain (n = 19 females, 19 males), Eye (n = 16 females, 16 males) and Lung (n= 16 females, 16 males). The X-inactivated gene Rps4x is used as a negative control, while Xist is taken as a female-specific control. The heights of the bars represent mean female expression (yellow bars) as relative to mean male expression (blue bars). Error bars signify +/- standard error of the mean. p-values: * ≤ 0.05, ** ≤ 0.01, *** ≤ 0.001 (two-sided unequal variance t-test), ns: not significant, non-significant p-values are given within brackets. The numbers 1-4 above the figure correspond to the four female-biased clusters in Figure 3.