  We study the low-energy consequences of the mass and mixing angle relations
in grand unified theories (GUT), which follow from an assumption that some
quarks and leptons are placed in the same GUT multiplets. This assumption is a
simple extension of that for the well-known bottom/tau mass ratio, which is one
of the most successful predictions of grand unification of matter multiplets.
We show that imposing the GUT relations leads naturally to a limited parameter
space from the large lepton mixing between the second and third generations.
