  In the context of the supersymmetric unification model in which the massless
sector contains extra particles beyond those in the minimal supersymmetric
standard model, we obtain mixings between quarks (leptons) and the extra
particles which are closely intertwined with Yukawa hierarchies. With the
assumption that the unification gauge group $G$ includes $SU(2)_R$, it is shown
that the non-trivial texture of the CKM matrix originates from the
extra-particle mixings. The CKM matrix of quarks emerges as a consequence of
the mixings between the down-type quarks and colored Higgses, both of which are
$SU(2)_L$-singlets. On the other hand, the CKM matrix of leptons is due to the
mixings stemming from the seesaw mechanism with the hierarchical Majorana mass
matrix of right-handed neutrinos.
