The morphological and genetic studies of the bramutant of Arabidopsis thaliana(L.) Heynh. from the collection of the Department of Genetics and Breeding, Moscow State University, showed that the BRAgene controls the major stages of inflorescence development: it suppresses the development of leaves subtending flowers (bracts) and inhibits the formation of the terminal flower. Inactivation of the BRAgene leads to the transition from the indeterminate bractless inflorescence characteristic of the family Cruciferaceae to the determinate bracteose inflorescence. It is suggested that the BRAgene is a regulator gene probably involved in the conversion of the bracteose determinate inflorescence to the indeterminate ebracteate inflorescence during the origin of ancestral crucifers.