Figure 4

Accounting for the occurrence of pleiotropy. One unbranched pathway is coupled to another by a conserved metabolite pair p and q. Such coupling is not uncommon in cellular systems and is one source of pleiotropy. Mutation of any one enzyme in one pathway will affect both fluxes (J_a and J_b) to a trait component and the concentrations of those trait components. See also Figure 5. Figure 4, like Figure 1, illustrates the need to adopt a systemic approach in attempts to understand the responses of a metabolising system to changes in any enzyme activity brought about by mutation.