  We consider the scenario in which the mass matrices of the charged fermions
in the SO(10) Grand Unified Theory are generated exclusively by renormalizable
Yukawa couplings to one $\mathbf{10} \oplus \mathbf{120}$ representation of
scalars. We analyze, partly analytically and partly numerically, this scenario
in the three-generations case. We demonstrate that it leads to unification of
the $b$ and $\tau$ masses at the GUT scale. Testing this scenario against the
mass values at the GUT scale, obtained from the renormalization-group evolution
in the minimal SUSY extension of the Standard Model, we find that it is not
viable: either the down-quark mass or the top-quark mass must be
unrealistically low. If we include the CKM mixing angles in the test, then, in
order that the mixing angles are well reproduced, either the top-quark mass or
the strange-quark mass together with the down-quark mass must be very low. We
conclude that, assuming a SUSY SO(10) scenario, charged-fermion mass generation
based exclusively on one $\mathbf{10} \oplus \mathbf{120}$ representation of
scalars is in contradiction with experiment.
