Inheritance of disarticulation in progenies of hybrids among Tibetan weedrace (9053 and AS907 of Triticum aestivum var. tibetanum), Yunnan hulled wheat (AS338 of T. aestivum concv. yunnanense) and spelt wheat (AS326 of T. aestivum concv. spelta) was studied. Disarticulation type is governed by some disarticulation modifying genes. These modifying genes can be divided into two groups, that is, wedge modifying genes (Wm) and barrel modifying genes (Bm). The two kinds of genes are codominant. Wedge type disarticulation is governed by the complement of at least two dominant wedge modifying genes (Wm1 and Wm2, Wm3 and Wm4, or Wm5 and Wm6). Barrel type disarticulation is controlled by at least one dominant barrel modifying gene (Bm1, Bm2 or Bm3) and its expression can be inhibited in certain genetic backgrounds. As to the background inhibition that dominant barrel modifying genes cannot express in some homozygous brittle rachis wheat, the hypothesis of epistasy of many homozygous alleles was suggested.