Fermion masses and mixing in models with SO(10) X A4 symmetry

We study the flavor sector in models where the three families of matter are unified in a (16, 3) representation of the SO(10) X A(4) group. The necessary ingredients to realize tribimaximal mixing in the lepton sector are identified systematically. The nonrenormalizable operators contributing to the fermion mass matrices play an important role. We also present a mechanism to explain the interfamily mass hierarchy of quarks and charged leptons, which relies on a universal seesaw'' mechanism and is compatible with tribimaximal mixing.