  We propose a supersymmetric (SUSY) SU(5) Grand Unified Theory (GUT) including
a single right-handed neutrino singlet and an adjoint matter representation
below the GUT scale and extend this model to include an A4 family symmetry and
a gauged anomaly-free Abelian group. In our approach hierarchical neutrino
masses result from a combined type I and type III seesaw mechanism, and the A4
symmetry leads to tri-bimaximal mixing which arises indirectly. The mixing
between the single right-handed neutrino and the matter in the adjoint is
forbidden by excluding an adjoint Higgs, leading to a diagonal heavy Majorana
sector as required by constrained sequential dominance. The model also
reproduces a realistic description of quark and charged lepton masses and quark
mixings, including the Georgi-Jarlskog relations and the leptonic mixing sum
rules s=r*cos(delta) and a=-r^2/4 with r=theta_C/3.
