English: Fundamental equations of quasispecies and representation of mutant spectra. The equations are the mathematical expression of the major concepts implied by quasispecies theory. The first equation describes the change of concentration of molecule i as a function of replication parameters, and its production from other molecules of the same ensemble. The second equation is the error threshold relationship, indicating the maximum amount of information (ʋmax) and the maximum average error rate max (p =1- q; q is the copying fidelity) for maintenance of genetic information. Terms are defined in the box on the right. Below, an evolving mutant spectrum (with mutations represented as symbols on the genomes), with an invariant consensus sequence (bottom). Details in ^[1]. Figure adapted from ^[2] with permission from the American Society for Microbiology, Washington DC, USA.