  The supersymmetric $SU(6)$ model equipped by the flavour-blind discrete gauge
symmetry $Z_3$ is considered. It provides simultaneous solution to the
doublet-triplet splitting problem, $\mu$-problem and leads to natural
understanding of fermion flavour. The Higgs doublets arise as Goldstone modes
of the spontaneously broken {\em accidental} global symmetry $SU(6)\times U(6)$
of the Higgs superpotential. Their couplings to fermions have peculiarities
leading to the consistent picture of the quark and lepton masses and mixing,
without invoking the horizontal symmetry or zero texture concepts. In
particular, the only particle that has direct $O(1)$ Yukawa coupling with the
Higgs doublet is top quark. Other fermion masses arise from the higher order
operators, with natural mass hierarchy described in terms of small ratios
$\eps_\Sigma=V_\Sigma/V_H$ and $\eps_H=V_H/M$, where $V_H$ and $V_\Sigma$
correspondingly are the $SU(6)$ and $ SU(5)$ symmetry breaking scales, and $M$
is a large (Planck or string) scale. The model automatically implies $b-\tau$
Yukawa unification. Specific mass formulas are also obtained, relating the down
quark and charged lepton masses. Neutrinos get small ($\sim 10^{-5}\,$eV)
masses which can be relevant for solving the solar neutrino problem via long
wavelength vacuum oscillation.
