  We present a mechanism able to generate the perturbatively absent up/down
$<{\bf 10} \cdot {\bf 10} \cdot {\bf 5}^H>$ quark Yukawa couplings of
SU(5)/flipped SU(5) GUTS in Type II orientifold compactifications with
D-branes. The mechanism works when there are Sp(N) gauge groups involved. The
${\bf {\bar 5}}$'s get charged under the Sp(N) gauge groups and the generation
of quark masses proceeds via the generation of the fermionic Sp(N) singlet
condensate $<{\bf {\bar 5} \cdot {\bar 5} \cdot {\bar 5} \cdot {\bar 5}}>$ in
the term $(1/{M_s^5}) {\bf 10} \cdot {\bf 10} \cdot < {\bf {\bar 5} \cdot {\bar
5} \cdot {\bar 5} \cdot {\bar 5}}>$. Also non-chiral states charged under Sp
gauge groups may become constrained by the requirement of Sp's becoming
strongly coupled.
