  Starting with high scale mixing unification hypothesis, we investigate the
renormalization group evolution of mixing parameters and masses for Dirac type
neutrinos. Following this hypothesis, the PMNS mixing angles and phase are
taken to be identical to the CKM ones at a unifying high scale. Then, they are
evolved to a low scale using renormalization-group equations. The notable
feature of this hypothesis is that renormalization group evolution with
quasi-degenerate mass pattern can explain largeness of leptonic mixing angles
even for Dirac neutrinos. The renormalization group evolution "naturally"
results in a non-zero and small value of leptonic mixing angle $\theta_{13}$.
One of the important predictions of this work is that the mixing angle
$\theta_{23}$ is non-maximal and lies only in the second octant. We also derive
constraints on the allowed parameter range for the SUSY breaking and
unification scales for which this hypothesis works. The results are novel and
can be tested by present and future experiments.
