  The observed hierarchy of quark and lepton masses and mixings may be obtained
by adding an abelian family symmetry to the Minimal Supersymmetric Model and
coupling quarks and leptons to an electroweak singlet scalar field. In a large
class of such models, this symmetry suffers from anomalies which must be
compensated by the Green-Schwarz mechanism; this in turn fixes the electroweak
mixing angle to be $\sin^2 \theta_W = 3/8$ at the string scale, without any
assumed GUT structure. The analysis is extended to two distinct generalisations
of the Standard Model: neutrino masses and mixings and R-parity violating
interactions.
