(Top) Schematic representation of the equilibria governing the reaction of the selector with a single-phage clone with a displayed peptide that binds the selector with a monovalent dissociation equilibrium constant of K_D. The simplifying kinetic assumptions are explained in the text. (Bottom) Graph showing the fraction of a clone's virions with one or two selector molecules bound to the virion's displayed peptides at equilibrium, as a function of the ratio of the dissociation equilibrium constant for these peptides to the concentration of the selector. The simplifying kinetic assumptions underlying the calculation are explained in the text.