Right-handed neutrinos with mass of O(10(12) - 10(13)) GeV are require
d to implement the seesaw mechanism and generate neutrino masses capab
le of playing a role in structure formation. Moreover models of fermio
n masses often relate the Yukawa couplings involving these neutrinos t
o the up-quark Yukawa couplings. Here we study the effects of such cou
plings on the radiative corrections to quark masses. We find that b -
tau equality at M(GUT) may still give the correct m(b)/m(tau)-ratio at
low energies, but only if there is large mu - tau mixing in the charg
ed leptonic sector. We propose specific mass matrix ''textures'' dicta
ted by a U(1) family symmetry whose structure preserves m(b) = m(tau)
at M(GUT). In these schemes, due to the large nu(mu) - nu(tau) mixing,
it is possible to give a simultaneous solution to the solar neutrino
deficit and the atmospheric neutrino problem.