The Origins of Evolutionary Innovations by Andreas Wagner

Author:Andreas Wagner
Language: eng
Format: epub
Publisher: Oxford University Press
Published: 2011-06-30T16:00:00+00:00

Figure 9.3 Gene duplications increase the size of the search space for novel phenotypes. The left and right parallelograms stand for the genotype space associated with each of two duplicate genes. Inscribed into the parallelograms are the genotype networks of each duplicate’s phenotype, with gray circles corresponding to genotypes with the same phenotype, and gray lines indicating neighboring genotypes. Symbols of different shapes and shading indicate genotypes with novel phenotypes that are only one mutation away from the genotype network shown. The two open circles in the middle stand for two hypothetical identical duplicate genes immediately after duplication. The identical protein structures (from chorismate mutase, Protein Data Bank identifier: 2gtv, [201] are shown merely to indicate that after a duplication that creates identical duplicates, the duplicates’ phenotypes will be identical. The jagged black lines illustrate that each duplicate mutates independently, and thus explores genotype space independently from the other duplicate.

Taken together, these observations show that the kind of robustness caused by gene duplications can increase access to novel phenotypes. But as if this was not enough, gene duplications also solve another problem that is common in evolutionary innovation: an old function of a system may need to be preserved not only during exploration of genotype space, but also afterwards, after a genotype with a novel function has been found. And often, a single genotype may not be able to execute both functions, or execute them equally well. A candidate example would be an enzyme that needs to catalyze reactions with two different substrates at high rate, or a regulatory protein that needs to bind two very different DNA sequences with high specificity. Here, gene duplications can preserve the old function of one duplicate, while facilitating not only the origin, but also the optimization of a novel function in the other duplicate [56, 135, 328].

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