  In supersymmetric grand unified theories (GUTs) based on S^1/(Z_2 x Z'_2)
orbifold constructions in 5 dimensions, Standard Model (SM) matter and Higgs
fields can be realized in terms of 5d hypermultiplets. These hypermultiplets
can naturally have large bulk masses, leading to a localization of the zero
modes at one of the two branes or to an exponential suppression of the mass of
the lowest-lying non-zero mode. We demonstrate that these dynamical features
allow for the construction of an elegant 3-generation SU(5) model in 5
dimensions that explains all the hierarchies between fermion masses and CKM
matrix elements in geometrical terms. Moreover, if U(1)_\chi (where SU(5) x
U(1)_\chi \subset SO(10)) is gauged in the bulk, but broken by the orbifold
action at the SM brane, the right-handed neutrino mass scale is naturally
suppressed relative to M_GUT. Together with our construction in the charged
fermion sector this leads, via the usual see-saw mechanism, to a realistic
light neutrino mass scale and large neutrino mixing angles.
