THE B-CHROMOSOME SYSTEM OF INNER MONGOLIAN AGROPYRON GAERTN .3. CYTOGENETICAL EVIDENCE FOR B-A PAIRING AT METAPHASE-I

During the course of cytogenetical studies of populations of Agropyron collected in Inner Mongolia, one chromosome possessing the traits of Agropyron B chromosomes, but able to pair with either an A chromosome or a B chromosome, was found in four plants. It was acrocentric and mi totically unstable. Cytological analysis at meiosis revealed that the B-A associations were of the end-to-end type involving the long arm of the B in 44 % of the cells during diakinesis. These B-A associations could remain up to metaphase I in half of the cases, although true chi asmata did not seem to be involved. The interest of this special B chr omosome in the study of the origin and evolution of B chromosomes is d iscussed.