The brittle rachis of the Tibetan weedrace (Triticum aestivum var. tibetanum) was found to be governed by a single dominant gene on the short arm of chromosome 3D. The new brittle rachis gene was designated Br1. This study also discovered that the type of disarticulation is governed by many genes that may differ from brittle rachis genes. In other words, the same brittle rachis gene may exhibit various types of disarticulation in various genetic backgrounds. So, after the brittle rachis gene (barrel type) in Aegilops tauschii entered hexaploid wheat through the amphidiploid path, it might exhibit the wedge type of disarticulation.