  We discuss the origin of Yukawa textures in the string-inspired and string
derived models based on the gauge group SU(4)xSU(2)_LxSU(2)_R supplemented by a
U(1)_X gauged family symmetry. The gauge symmetries are broken down to those of
the minimal supersymmetric standard model which is the effective theory below
10^16 GeV. The combination of the U(1)_X family symmetry and the Pati-Salam
gauge group leads to a successful and predictive set of Yukawa textures
involving two kinds of texture zeroes: horizontal and vertical texture zeroes.
We discuss both symmetric and non-symmetric textures in models of this kind,
and in the second case perform a detailed numerical fit to the charged fermion
mass and mixing data. Two of the Yukawa textures allow a low energy fit to the
data with a total chi^2 of 0.39 and 1.02 respectively, for three degrees of
freedom. We also make a first attempt at deriving the non - renormalisable
operators required for the Yukawa textures from string theory.
