Mutational robustness
Mutational robustness describes the extent to which an organism’s phenotype remains constant in spite of mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...

. Natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....

 can directly induce the evolution of mutational robustness only when mutation rate
Mutation rate
In genetics, the mutation rate is the chance of a mutation occurring in an organism or gene in each generation...

s are high and population size
Population size
In population genetics and population ecology, population size is the number of individual organisms in a population.The effective population size is defined as "the number of breeding individuals in an idealized population that would show the same amount of dispersion of allele frequencies under...

s are large. The conditions under which selection could act to directly increase mutational robustness are extremely restrictive, and for this reason, such selection is thought to be limited to only a few viruses and microbes having large population sizes and high mutation rates. However, mutational robustness may evolve as a byproduct of natural selection for robustness to environmental perturbations.

Mutational robustness is thought to be one driver for theoretical viral quasispecies
Viral quasispecies
A viral quasispecies is a group of viruses related by a similar mutation or mutations, competing within a highly mutagenic environment. The theory predicts that a viral quasispecies at a low but evolutionarily neutral and highly connected region in the fitness landscape will outcompete a...


Robustness and evolvability

Mutational Robustness appears to have a negative impact on evolvability
Evolvability is defined as the capacity of a system for adaptive evolution. Evolvability is the ability of a population of organisms to not merely generate genetic diversity, but to generate adaptive genetic diversity, and thereby evolve through natural selection.In order for a biological organism...

 because it reduces the mutational accessibility of distinct heritable phenotypes for a single genotype and reduces selective differences within a genetically diverse population. Counter intuitively however, it has been hypothesized that phenotypic robustness towards mutations may actually increase the pace of heritable phenotypic adaptation when viewed over longer periods of time. The hypothesis put forth is that connected networks of fitness neutral genotypes result in mutational robustness and reduced accessibility of heritable phenotypes over short timescales. On the other hand over longer periods of time, genetic drift combined with neutral/buffered mutations can provide mutational access to a greater number of distinct heritable phenotypes that are reached from different points of the genetic neutral network. This hypothesis is supported by simulations of biological systems. and appears consistent with the available data on biomolecular evolution Simulations have indicated that positive relationships between mutational robustness and evolvability can be facilitated by degeneracy
Degeneracy (biology)
Within biological systems, degeneracy refers to circumstances where structurally dissimilar components/modules/pathways can perform similar functions under certain conditions, but perform distinct functions in other conditions. Degeneracy is thus a relational property that requires comparing the...

within biological systems.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.