  Mixing of the pseudoscalar mesons is discussed in the quark-flavor basis. The
divergences of the axial vector currents which embody the axial vector anomaly,
combined with the assumption that the decay constants follow the pattern of
particle state mixing in that basis, determine the mixing parameters for given
masses of the physical mesons. These mixing parameters are compared in some
detail with results from other work. Phenomenological applications of the
quark-flavor mixing scheme are presented with particular interest focussed on
isospin symmetry breaking which is generated by means of eta and eta'
admixtures to the pion. Consequences of a possible difference in the basis
decay constants f_u and f_d for the strength of isospin symmetry breaking are
also examined.
