  In SO(10) models with a vectorial fourth generation of down quarks and
leptons, the structure of the neutrino Majorana and Dirac mass matrices
generically coincide with those of up- and down-quarks, respectively. Then the
small neutrino mass hierarchy follows from the mismatch of the up and down
quark mass hierarchies and we can accommodate naturally a normal hierarchy. The
effective CP violating phases in the quark sector, neutrino oscillations and
leptogenesis are unrelated.
