  We discuss the possibility of unifying in a simple and economical manner the
Yukawa couplings of third generation fermions in a non-supersymmetric SO(10)
model with an intermediate symmetry breaking, focusing on two possible patterns
with intermediate Pati-Salam and minimal left-right groups. assume a minimal
Yukawa sector at high energy, starting with two Higgs bi-doublets at the
intermediate scale which then simply reduce to a two Higgs doublet model at the
electroweak scale. We first enforce gauge coupling unification at the two-loop
level by including the threshold corrections in the renormalisation group
running which are generated by the heavy fields that appear at the intermediate
symmetry breaking scale. We then study the running of the Yukawa couplings of
the top quark, bottom quark and tau lepton at two-loops in these two breaking
schemes, when the appropriate matching conditions are imposed. We find that the
unification of the third family Yukawa couplings can be achieved while
retaining a viable spectrum, provided that the ratio of the vacuum expectation
values of the two Higgs doublet fields is large, $\tan\beta \approx 60$.
