It is proposed that the relationship $\frac{{m}_{u}}{{m}_{d}}=\frac{{m}_{s}}{{m}_{c}}$ is a zeroth-order relationship of the spontaneously broken Lagrangian. This relationship is achieved by a symmetry which exchanges fields of different charges, and SU(2)\ifmmode\times\else\texttimes\fi{}U(1)\ifmmode\times\else\texttimes\fi{}U(1) is the smallest extension of SU(2)\ifmmode\times\else\texttimes\fi{}U(1) by which one can implement such an exchange symmetry. Extended to leptons, the scheme achieves $\frac{{m}_{e}}{{m}_{\ensuremath{\mu}}}\ensuremath{\sim}\frac{{m}_{d}}{{m}_{c}}=\frac{{m}_{u}}{{m}_{s}}$ in a natural way. Limited to light quarks and leptons and the Higgs particles to which they couple, the model considered has identical neutral-current parametrization to the standard Weinberg-Salam model. When heavy quarks and leptons are introduced, and an extra Higgs field is added to provide their masses, the neutral-current parametrization is modified. The limit to the Weinberg-Salam case is discussed. Various sets of parameter values can be chosen which provide an adequate description of neutrino scattering data, polarized electron scattering from deuterium, and any one of the results of the different atomic parity violation experiments in bismuth.