In the decomposition of SO(10) grand unification to SU(5)×U(1)χ, two desirable features are obtained with the addition of one colored fermion octet Ω, one electroweak fermion triplet Σ and one complex scalar triplet S to the particle content of the standard model with two Higgs doublets. They are (1) gauge coupling unification of SU(3)C×SU(2)L×U(1)Y to SU(5), and (2) the automatic (predestined) emergence of dark matter, i.e., Ω, Σ and S, with dark parity given by (−1)Qχ+2j. It suggests that U(1)χ may well be the underlying symmetry of the dark sector.