  TThe problem of fermion masses hierarchy in the Standard Model is considered
on a toy model of a 10-dimensional space-time with a IIA supergravity type
background. Dirac equation on this background, after compactification of extra
4- and 1-dimensional subspaces, gives the spectrum of Fermi fields which
profiles in 5 dimensions and corresponding Higgs generated masses in 4
dimensions depend on the eigenvalues of Dirac operator on the named compact
subspaces. Schwarzschild Euclidean deformation of the supergravity throat with
the "apple-shaped" conical singularity permits to leave only three
non-divergent angular modes interpreted as three generations of the down-type
quarks. Calculated ratio $m_{d} / m_{s} = e^{-3}$ exactly coincides with its
experimentally observed value for integer values of two free parameters of the
10-dimensional background. Equations for non-chiral modes coincide with the
non-relativistic Schr\"odinger equation for an electron moving in a Coulomb
field; the corresponding small fermion masses generated by the twisted boundary
conditions are expressed through the degenerate hypergeometric functions.
