Table 1. Analytically obtained epistasis values for various mutation numbers in the simple, ten-node two-pathway model (Figure 1A) for equal (5+5) and unequal (8+2) path lengths.

		Equal path lengths (5+5)			Unequal path lengths (8+2)
Mutation number	Possible epistasis values	Frequency	Mean	Variance	Frequency	Mean	Variance
2	−0.250	50.0%	0	0.250	32.0%	0.090	0.234
	0.250	50.0%			68.0%
4	−0.063	87.5%	0	0.165	58.9%	0.143	0.246
	0.438	12.5%			41.1%
7	−0.008	98.4%	0	0.062	79.0%	0.097	0.204
	0.492	1.6%			21.0%
10	−0.001	99.8%	0	0.022	89.3%	0.053	0.155
	0.499	0.2%			10.7%

The case of equal path lengths corresponds to the null model (see text). For each mutation number, the two possible epistasis values, the frequency of each, mean epistasis and its variance are shown. Analytical results were cross-checked against simulations to confirm the consistency of the two approaches (not shown).