Table 1.

Results obtained from epistasis analysis of examples in Figure 3.

Gene state/mutation	X	Y	Z
x	0	0	0
y	1	0	0
xy	0	0	0
WT	1	1	1

The results for all the examples are the same shown in the table. The examples of Figures 3B,C,D have some extra interactions than the one shown in Figure 3A, but we could not detect these extra interactions with the epistasis analysis alone. Is important to note, that even when Huang and Sternberg (2006) advise us that we cannot order genes with the same phenotype in this kind of pathways, we can do it here with the table. This is because we observe that when X is mutated we obtain the same values for X, Y, and Z as in the double mutant of X and Y. Moreover, the presence of X in Y mutant could indicate the presence of a substrate product of X activity (as could be assumed in Huang and Sternberg, 2006) indicating that X is epistatic to Y and hence is upstream of Y.