Radiative quark masses constrained by the gauge group only

We discuss the possibility of obtaining the observed pattern of quark masses and mixings as a consequence of radiative corrections, gauge invariance and particle content of the theory. We do not allow any kind of additional symmetry, such as family and discrete symmetries. A model based on the gauge groupSU(3)×SU(2) _L ×SU(2) _R ×U(1) _B?L is considered. It turns out that the correct values of quark masses can be reasonably reproduced. The typical strength of the flavour changing couplings of theZ ⁰-boson is however at least one order of magnitude above the experimental upper bounds. A comparison is made with a model in which an additional discrete symmetry is present. In this case flavour changing phenomena can be kept under control.