  Right handed neutrinos with mass of ${\cal O} \; (10^{12}-10^{13})$ GeV are
required to implement the see-saw mechanism and generate neutrino masses
capable of playing a role in structure formation.
  Moreover models of fermion masses often relate the Yukawa couplings involving
these neutrinos to the up-quark Yukawa couplings. Here we study the effects of
such couplings 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
charged leptonic sector. We propose specific mass matrix ``textures'' dictated
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.
