  We perform a general 1-loop analysis by adding extra matter to the SM
content, as well as by allowing a non-standard U(1)Y normalization in order to
achieve unification. We find numerous solutions with U(1)Y only charged extra
matter and unification scale of the order of MU=10^{16} GeV, or with SU(2)
charged extra matter with lower MU. We next identify the SM extra matter as
originating from the breaking of SO(10) either through the Pati-Salam group
SU(4)xSU(2)LxSU(2)R or the flipped SU(5). In both cases, unification can be
achieved with a rather minimal extra content. Contrary to the one-step SU(5)
unification, in the two-step SO(10) unification we are discussing, coulored
extra matter is not necessary. Finally, we discuss a split-supersymmetry like
case, where extra matter is added to the split supersymmetric spectrum in order
to attain 1-loop unification.
