It has been proposed recently that magnetic field reversals result from the coupling between two magnetic modes, one of dipolar symmetry and another one of quadrupolar symmetry. As far as planetary magnetic fields are concerned, this linear coupling occurs when the equatorial symmetry of the problem is broken by the flow. We performed analytical computations of alpha² spherical dynamos. The dipolar and quadrupolar modes are computed from the induction equation. When the alpha effect breaks the equatorial symmetry, these modes get coupled and exhibit either reversals or localization of the magnetic field in only one of the two hemispheres of the planet. The first regime corresponds to the Earth' magnetic field reversals, whereas the second one could describe Mars' magnetic field, which is sometimes claimed to have been localized in the southern hemisphere of the planet only. We will discuss these two different behaviors in the framework of low-dimensional dynamical systems.