Speltoid mutants, which have slender spikes, were found in the offspring of a cross, euploid common wheat, Triticum aestivum cv. ‘Chinese Spring’ (♀)× an alien addition line of Chinese Spring having the long arm of an Aegilops longissima chromosome. With the offspring of three of these speltoid mutants, chromosome mapping was conducted for a speltoid suppression gene Q of common wheat. The ... [Show full abstract] C-banding study demonstrated that the speltoid character was always associated with partial deletions in the long arm of chromosome 5A. The abnormal 5A with the least deletion retained the intercalary C-band which was located at about 54 per cent of the long arm from the centromere. Therefore, it was properly decided that the Q gene was situated somewhere in the distal 46 per cent region of the 5A long arm.