  Using approximately 4.3 million hadronic Z^0 decays collected with the OPAL
detector at LEP between 1990 and 1995, we measure the branching fractions of
the Z^0 into up-type and down-type light quarks, R_q, and the forward-backward
asymmetries, A_FB(q), using high-momentum stable particles as a tag. Adopting a
method that employs double tagged events to determine the flavour tagging
efficiencies, and assuming the flavour independence of strong interactions and
SU(2) isospin symmetry, we measure: R_{d,s}/(R_d + R_u + R_s) = 0.371 +/-
0.016(stat.) +/- 0.016(syst.) and A_FB(d,s) = 0.068 +/- 0.035(stat.) +/-
0.011(syst.), assuming the branching fractions and forward-backward asymmetries
of down and strange quarks to be equal. The results are essentially free of
assumptions based on hadronisation models. These results are in agreement with
the Standard Model expectations and are used to infer the left and right handed
couplings of strange/down quarks to the Z^0, yielding g_L^{d,s} =
-0.44^{+0.13}_{-0.09} and g_R^{d,s} = +0.13^{+0.15}_{-0.17}. The results for
the up quark, R_u/(R_d + R_u + R_s) = 0.258 +/- 0.031(stat.) +/- 0.032(syst.)
and A_FB(u)= 0.040 +/- 0.067(stat.) +/- 0.028(syst.), are fully negatively
correlated and almost completely positively correlated, respectively, with the
corresponding down-type results.
