Figure 3

Score distributions for fission-yeast genes that are ranked below the cycling score threshold. The red curve is the distribution of 350 fission-yeast orthologs of cycling budding-yeast genes. The black curve is the distribution of all the other 3,641 fission-yeast genes. Density is the distribution density for each of the different scores. As can be seen, the red curve is highly skewed to the right (higher score). In fact, the difference between the two curves is significant, with a p-value of 0.01 (Wilcoxon rank-sum test). Thus, while orthologs of cycling budding-yeast genes may fall just below the fission-yeast threshold, they are still at least weakly cycling, much more so than expected by chance, indicating that expression is conserved at a much stronger rate than the rate determined by thresholding-based methods.