2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/205522We review the prototype model of a grand unified theory on the orbifold $S^1/Z_2$ and discuss topics related to the choice of boundary conditions; the dynamical rearrangement of gauge symmetry and the equivalence classes of BCs. We explore a family unification scenario by orbifolding.19 pages, 4 figures, to appear in the proceeding of International Workshop on Grand Unified Theories: Current Status and Future Prospects (GUT07), December 17-19 2007, Kusatsu, JapanHigh Energy Physics - Phenomenologytext