  We propose a model based on the gauge group $SU(4)\times SU(2)_L\times
SU(2)_R$ where the Dirac masses of all the known fermions are generated as
one-loop radiative corrections. We are able to generate realistic quark and
lepton masses and mixings without a large hierarchy of Yukawa couplings or
extra symmetries. The neutrino masses, which are see-saw suppressed, lie in the
mass range favored to solve the solar neutrino problem. The importance of
threshold corrections to tree-level mass relations in certain
non-supersymmetric GUTs is demonstrated.
