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Figure 5 | BMC Evolutionary Biology

Figure 5

From: Proportionality between variances in gene expression induced by noise and mutation: consequence of evolutionary robustness

Figure 5

Change in the variances after the switching of the fitness condition. After evolution under the fitness condition to favor x i >0 ("on") for all the target genes i = 1, 2, ... k(= 8) as studied already, the fitness condition was switched at a certain generation to favor x i >0 for i = 1, 2, .., k/2 and x i <0 for i = k/2 + 1, .., k (i.e., the fittest gene expression pattern was given by + + + + − − −−, instead of + + + + + + ++). The switching was applied after a sufficiently large number of generations when the fittest networks are evolved (i.e., with x i >0 for the target genes). The switch initially caused a decrease in the fitness, but after a few dozens of generations, almost all networks evolved to adapt to the new fitness condition if σ > σ c . The values of the parameter and the procedure for computing the variances were identical with those in the previous cases. (i) The plot of the variances of the fitness, V g versus V ip per generation after the switching of the fitness condition. The color represented the generation number from the switching. There was a correlation between the increase in both the variances after the switch, and then, there was a proportional decrease as adaptation to the new fitness condition progressed. (b)(c) The plot of (V g (i) and V ip (i)) over all genes i at the generation 10, 20, and 30 for (b), and 60, 80, and 120 for (c). After the switch V g (i) and V ip (i) increased up to 30-60 generations, while the ratio V g (i)/V ip (i)approached unity for many genes. For generations >60, the variances decreased while the proportionality between V g (i) and V ip (i) was regained.

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