  We study neutrino masses and mixings based on the simplest SO(10) mass
relations and the seesaw mechanism. We find that the requirement of large
neutrino mixings determines the relative magnitude of the heavy Majorana
neutrino masses in terms of the known quark mass hierarchy. This leads to
specific predictions for the structure of the neutrino mixing matrix, the light
neutrino masses, CP violation in neutrino oscillations, neutrinoless double
b-decay and the baryon asymmetry.
