Total and differential cross sections for the reactions Ô · ¿ He · Ñ ¼ with Ñ and Ô · ¿ H· · were measured with the GEM detector at COSY for beam momenta between threshold and the maximum of the corresponding baryon resonance. For both reactions a strong forward-backward asymmetry was found. The data were compared with model calculations. The aspect of isospin symmetry breaking is studied.