Table 1.

Glossary.

Adaptations: properties (or phenotypes) that increase the fit of the organism to its environment and which are favored by natural selection.
Degree distribution: gives the probability, P(k), that a selected node in the network has exactly k links (i.e., number of connections with other nodes).
Dispensable gene: a gene whose deletion (or inactivation) does not have a detectable fitness effect.
Enzyme kinetics: study of metabolic (biochemical) reactions in terms of rates.
Fitness landscape: visualizes the relationship between genotype and fitness. The plane of the landscape contains all possible genotypes in such a way that similar genotypes are located close to each other on the plane and the height of the of the landscape reflects the fitness of the corresponding genotype.
Genetic drift: stochastic changes in allele frequencies in a population that occur owing to random sampling effects in the formation of successive generations.
Metabolic flux: turnover rate of substrates through metabolic reactions or pathways.
Mutation accumulation experiments: spontaneous mutations are allowed to accumulate over many generations by ensuring a very small effective population size where genetic drift overwhelms natural selection (hence the sampling of mutations is nearly unbiased).
Mutational robustness: phenotypic constancy in the face of mutations.
Natural selection: the process by which favorable heritable properties of individuals become more common (and unfavorable traits become less common) in successive generations of a population of reproducing organisms.
Network diameter: the average shortest distance (or minimal number of links) between any two nodes in the network. Scale-free networks show small diameters due to the existence of highly connected nodes.
Scale-free network: a network whose degree distribution follows a power law, i.e., P(k)∼k−γ (that is, it contains a small number of highly connected nodes (called “hubs”) and a high number of nodes with few links).
Trade-off (in evolutionary biology): two traits are in trade-off relation when an increase in fitness due to a change in one trait is opposed by a decrease in fitness due to a concomitant change in the second trait.
Yield: a ratio indicating how many moles of product are obtained per mole of substrate used.