  We present a common explanation of the fermion mass hierarchy and the large
lepton mixing angles in the context of a grand unified flavor and gauge theory
(GUTF). Our starting point is a SU(3)xU(1) flavor symmetry and a SO(10) GUT, a
basic ingredient of our theory which plays a major role is that two different
breaking pattern of the flavor symmetry are at work. On one side, the dynamical
breaking of SU(3)xU(1) flavor symmetry into U(2)xZ_3 explains why one family is
much heavier than the others. On the other side, an explicit symmetry breaking
of SU(3) into a discrete flavor symmetry leads to the observed tribimaximal
mixing for the leptons. We write an explicit model where this discrete symmetry
group is A4. Naturalness of the charged fermion mass hierarchy appears as a
consequence of the continuous SU(3) flavor symmetry. Moreover, the same
discrete A4-GUT invariant operators are the root of the large lepton mixing,
small Cabibbo angle, and neutrino masses.
