  We compare N-body simulations of isolated galaxies performed in both
frameworks of modified Newtonian dynamics (MOND) and Newtonian gravity with
dark matter (DM). We have developed a multigrid code able to efficiently solve
the modified Poisson equation derived from the Lagrangian formalism AQUAL. We
take particular care of the boundary conditions that are a crucial point in
MOND. The 3-dimensional dynamics of initially identical stellar discs is
studied in both models. In Newtonian gravity the live DM halo is chosen to fit
the rotation curve of the MOND galaxy. For the same value of the Toomre
parameter (Q_T), galactic discs in MOND develop a bar instability sooner than
in the DM model. In a second phase the MOND bars weaken while the DM bars
continue to grow by exchanging angular momentum with the halo. The bar pattern
speed evolves quite differently in the two models: there is no dynamical
friction on the MOND bars so they keep a constant pattern speed while the DM
bars slow down significantly. This affects the position of resonance like the
corotation and the peanut. The peanut lobes in the DM model move radially
outward while they keep the same position in MOND. Simulations of (only
stellar) galaxies of different types on the Hubble sequence lead to a
statistical bar frequency that is closer to observations for the MOND than the
DM model.
