Fermion Masses from Superstring Models with Adjoint Scalars
  We explore the possibility of embedding supersymmetric GUT texture ideas into superstring models. We discuss the construction of GUT models using free fermionic strings. We find SO(10) models with adjoint scalars, three generations of chiral fermions, and a fundamental Higgs with a Yukawa coupling to only the third generation. 
Shyamoli Chaudhuri, Stephen-wei Chung, and Joseph D. Lykken