  We systematically study the three family extension of the Pati-Salam gauge
group with an anomaly-free single irreducible representation which contains the
known quarks and leptons without mirror fermions. In the context of this model
we implement the survival hypothesis, the modified horizontal survival
hypothesis, and calculate the tree level masses for the gauge boson and fermion
fields. We also use the extended survival hypothesis in order to calculate the
mass scales using the renormalization group equation. The interacting
Lagrangean with all the known and predicted gauge interactions is explicitly
displayed. Finally the stability of the proton in this model is established.
