Figure 2

Connectivity of potential metabolisms can be inferred from parent and child relationship. The figure uses a hypothetical example of two neighboring metabolisms with three reactions each (upper panel) to illustrate the relationship between the connectedness of genotypes with n reactions (G(n)) and their “parents” of n + 1 reactions that can be obtained from them by adding a single reaction (lower panel). Importantly, if genotypes G(n) form a connected set, then all genotypes G(n + 1) obtained by adding one reaction to each of them also form a connected set.