Organization of cell assemblies in the hippocampus

perhaps in the context of a diploid model analogous to the haploid one presented here. Hsp90 might be a member of a fairly large class of genes with the ability to serve as evolutionary capacitors, most of which might have more subtle effects than Hsp90 has. The existence of this complementary set of capacitors means that adaptation by means of the release of canalized variation might be possible even under conditions that do not involve chronic environmental stress, such as sexual selection and predator–prey 'arms races'. The proposed capacitance mechanism could be tested by the analysis of genotypic and phenotypic data from populations of a laboratory microorganism , such as S. cerevisiae or Escherichia coli, at successive stages in adaptation to an artificial selection regime. As for natural adaptations , establishing the role of Hsp90 or another potential capaci-tor in facilitating the evolution of any particular trait will require intensive investigation of the relevant ecological, population-biological and evolutionary-genetic history. A Methods Gene networks and their evolution were modelled as described previously 14. The original model, and extensions of it used here, are described fully in Supplementary Information. The yeast gene-expression data are from ref. 20. The statistical tests presented use the same stringent criterion for declaring a gene a regulatory target of the knocked out gene as that used by those authors. To ensure the robustness of our results we repeated the tests with a range of more lenient criteria; in all cases the test results remained significant. Details of our analysis, including a list of microarray experiments used, are also available in Supplementary Information. the evolution of genetic architecture: A continuum of alleles model with pairwise A £ A epistasis.