  We construct the SU(5) and SO(10) models from F-theory. Turning on the U(1)
fluxes, we can break the SU(5) gauge symmetry down to the Standard Model (SM)
gauge symmetry, and break the SO(10) gauge symmetry down to the SU(3)_C X
SU(2)_L X SU(2)_R X U(1)_{B-L} gauge symmetry. In particular, all the SM
fermion Yukawa couplings preserve the enhanced U(1)_a X U(1)_b gauge or global
symmetries at the triple intersections of the SM fermion and Higgs curves. And
the SM fermion masses and mixings can be generated in the presence of
background fluxes. In our models, the doublet-triplet splitting problem can be
solved naturally. The additional vector-like particles can obtain heavy masses
via the instanton effects or Higgs mechanism and then decouple at the high
scale. The SM gauge couplings at the string scale, which are splitted due to
the U(1) flux effects, can be explained by considering heavy threshold
corrections from the extra vector-like particles. Moreover, in the SU(5) model,
we have the Yukawa coupling unification for the bottom quark and tau lepton. In
the SO(10) models, we have the Yukawa coupling unification for the top and
bottom quarks, and the Yukawa coupling unification for the tau lepton and tau
neutrino.
