  We consider large classes of chiral extensions of the Standard Model,
including new quark generations that do not involve additional neutrinos as
well as lepton generations without quarks. An analysis of renormalization flows
of Yukawa and quartic scalar couplings reveals that additional quarks are not
compatible with a scenario of grand unification without violating the strong
bounds from direct and Higgs searches at colliders. Constraints from direct
searches, electroweak precision observables, and Higgs physics, together with
the assumption that additional new physics beyond the extended chiral field
content should enter significantly above the TeV scale, allows us to make
predictions for searches at the LHC.
