Fig. 4

Robustness of the RNA folding. a Single-stranded RNA molecule folds onto itself, to form stems and loops. b Mapping from the sequence space (left) to the phenotypic space (right) is many to few, meaning that many sequences fold into the same secondary structure. c Sequences that fold into the same structure and hence do not differ in their phenotype belong to neutral networks (yellow, green, red, blue), consisting of nodes connected by single mutational changes. Figures from Fontana (2002)