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Selection for robustness?
Eörs Szathmáry
Collegium Budapest
Eötvös University
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
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
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
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
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
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