MA plots for different 20% mixtures. M (log-fold change) versus A (intensity) for two 20% mixture difference comparisons: Mix 6-Mix 8 and Mix 2-Mix 4. Shown here is the HuEx data only. Genes expressed significantly higher in the pure heart samples (2,218) are shown in red and brain-expressed genes (1,782) are shown in green. In terms of the difficulty in detecting differential expression, the two 20% mixtures are very different.