A tinkerer's tales | Nature Reviews Genetics

The three articles examine the routes that evolution takes in creating an adaptive function. One study, by Prud'homme, Gompel and colleagues, concentrated on the black spot that exists on

the male wing of some Drosophila species. The wing spot has evolved independently in two lineages, where it is used to woo females, and in both cases the evolution of the pattern involves

the yellow pigmentation gene. What is most interesting is that the cis-regulatory elements that have been used in the two cases are distinct, indicating that evolution can use different

mechanisms to reach a convergent, adaptive endpoint.

The repeated use of the yellow gene in different lineages raises another theme in evolution — constraint. That constraint exists was the strong conclusion to emerge from the work of

Weinreich and colleagues when they addressed a related issue: how many paths can a protein take towards a fitter state? Their choice was the evolution of bacterial β-lactamase, which can

evolve a 100,000-fold increase in antibiotic resistance by acquiring just five point mutations. Of the 120 hypothetical trajectories to drug-resistant alleles, 102 are inaccessible to

evolution. This prediction was based on the probability of fixation of mutant combinations; in fact, the situation is more extreme than this, because of the 18 plausible combinations as few

as 2 are probable, indicating that the path to adaptive protein evolution is largely predictable.

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