  We investigate the renormalization group evolution of fermion masses, mixings
and quartic scalar Higgs self-couplings in an ${\it extended}$
non-supersymmetric SO(10) model, where the Higgs sector contains the ${\bf
10}_{\rm H}$, ${\bf 120}_{\rm H}$, and ${\bf 126}_{\rm H}$ representations. The
group SO(10) is spontaneously broken at the GUT scale to the Pati-Salam group
and subsequently to the Standard Model (SM) at an intermediate scale $M_{\rm
I}$. We explicitly take into account the effects of the change of gauge groups
in the evolution. In particular, we derive the renormalization group equations
for the different Yukawa couplings. We find that the computed physical fermion
observables can be successfully matched to the experimental measured values at
the electroweak scale. Using the same Yukawa couplings at the GUT scale, the
measured values of the fermion observables cannot be reproduced with a SM-like
evolution, leading to differences in the numerical values up to around 80 %.
Furthermore, a similar evolution can be performed for a ${\it minimal}$ SO(10)
model, where the Higgs sector consists of the ${\bf 10}_{\rm H}$ and ${\bf
126}_{\rm H}$ representations only, showing an equally good potential to
describe the low-energy fermion observables. Finally, for both the extended and
the minimal SO(10) models, we present predictions for the three Dirac and
Majorana CP-violating phases as well as three effective neutrino mass
parameters.
