Twenty‐two bivalents were observed in X117 oat (Avena sativa L.), a isogenic line resistant to crown rust (Puccinia coronata Cda. avenae Fraser and Led.), and with 42 + 2 fragment chromosomes. The homologous fragment chromosomes are either telocentric or acrocentric. Transmission through the egg, calculated from the backcross data, was 18.2%. A dominant gene, Pc‐15, conferring resistance to races 264 and 290 of crown rust of oats is located on each of the fragments.