  It is pointed out that in a seesaw quark mass matrix model which yields a
singular enhancement of the top-quark mass, the right-handed fermion-mixing
matrix U_R^u for the up-quark sector has a peculiar structure in contrast to
the left-handed one U_L^u. As an example of the explicit structures of U_L^u
and U_R^u, a case in which the heavy fermion mass matrix M_F is given by a form
[(unit matrix)+(rank-one matrix)] is investigated. As a consequence, one finds
observable signatures at projected high energy accelerators like the production
of a fourth heavy quark family.
