  In this work a mass model based on a SO(10) GUT with a global U(1) family
symmetry is discussed which leads to an asymmetric Nearest Neighbour
Interaction structure for the fermionic mass matrices. As a result of the
analysis one gets three solutions of the model which include several large
left- and right-handed fermion mixings. Those mixings are not observable in the
SM where only the CKM quark mixing matrix can be measured, but they have
testable effects on the branching ratios of nucleon decays in theories beyond
the SM. One finds that decay channels with positrons in the final state are
suppressed while channels with antimuons and antineutrinos are enhanced
compared to models with small mixings. The total nucleon lifetimes obtained
should be observable by future experiments. The SO(10) model also predicts the
masses and mixings of the light neutrinos. They are in the right range to
explain the anomalies of solar and atmospheric neutrinos by means of
oscillations, preferring the small angle MSW solution for the solar neutrino
deficit.
