  We present a detailed study of the quark and lepton mass spectra in a SO(10)
framework with one 10_H and one \bar{126}_H Higgs representations in the Yukawa
sector. We consider in full generality the interplay between type-I and type-II
seesaws for neutrino masses. We first perform a \chi^2 fit of fermion masses
independent on the detailed structure of the GUT Higgs potential and determine
the regions in the parameter space that are preferred by the fermion mass sum
rules. We then apply our study to the case of the minimal renormalizable SUSY
SO(10) GUT with one 10_H, one \bar{126}_H, one 126_H, and one 210_H Higgs
representations. By requiring that proton decay bounds are fulfilled we
identify a very limited area in the parameter space where all fermion data are
consistently reproduced. We find that in all cases gauge coupling unification
in the supersymmetric scenario is severely affected by the presence of lighter
than GUT (albeit B-L conserving) states. We then conclusively show that the
minimal supersymmetric SO(10) scenario here considered is not consistent with
data. The fit of neutrino masses with type-I and type-II seesaws within a
renormalizable SO(10) framework strongly suggests a non-SUSY scenario for gauge
unification.
