Fig 1.

Relative population numbers of binary sequences S_k (ordinate) as functions of single-digit error rate (1 − q) (abscissa). The length of all binary sequences is N = 20. All 2^N ≈ 10⁶ sequences are degenerate in their reproductivity except for one “master” sequence S_m, which reproduces 10 times more efficiently than the rest. The resulting quasispecies distribution is centered at the master sequence (“0” errors). The numbers 1, 2, … 20 refer to the sum of all 1-, 2-, … 20-error mutants. The red curve refers to the consensus sequence, which shows a sharp first-order phase transition at the error threshold.