Selection for robustness?

1. Selection for robustness? Eörs Szathmáry Collegium Budapest Eötvös University

2. Gene redundancy • Between 25 and 50% of genes in eukaryotes are duplicates • Duplication and divergence is fuel for evolvability • True evolvability: the capacity to arrive at innovations • More than 90% of yeast genes have no clear phenotypic consequence as knockouts • But they do not evolve fast: probably important rarely

3. Single-copy genes can also be dispensable • BUT duplicate genes tend to be more dispensable • Distributed robustness: an important concept • Metabolic and gene regilatory networks are good examples • Increasing gene redundancy decreases the control coefficient of the enzyme

4. Robustness: adaptation to mutations? • It is easier to find robust solutions, e.g. in protein space • Once such a solution is found, it can in pinciple be fine-tuned • It certainly happened for the genetic code • Selection for robustness is on the order of the mutation rate • Nu >> is a necessary condition (polymorphism) • Average time to fixation: 1/N

5. Selection • Populations must be polymorphic for robustness • Mutations have more deleterious effects in the less robust individuals • In an asexual system maximal robustness depends on the topoplogy of the neutral space • Mean fitness does not depend from the mutation rate only

6. Robutsness as an adaptation to environmental noise • Nongenetic change is always there • Chaperons act againts thermal noise AND mutations • Mutations are a relatively minor source of variation • The genetic code is robust against mistakes in translation

7. Robustness can be cotsly • Gene overlap in viruses decreases robustness but increases the replication rate • Communities can develop towards robustness • For any system with redundancy another solution with the same robustness but no redundancy exists