The pericentromeric heterochromatin of the grass Zingeria biebersteiniana (2n=4) is composed of Zbcen1-type tandem repeats that are intermingled withaccumulated dispersedly organized sequences

DNA reassociation and hydroxyapatite chromatography were used to isolate hi gh-copy DNA of the grass Zingeria biebersteiniana (2n = 4). In situ hybridi zation demonstrated that the DNA isolated was enriched for pericentromere-s pecific repetitive sequences. One abundant pericentromere-specific componen t is the differentially methylated tandem-repeat family Zbcen1. Other seque nces isolated, Zb46 and Zb47A, are dispersed and display similarity to part s of the gypsy- and copia-like retrotransposable elements of other grasses. In situ hybridization with the copia-like sequence Zb47A resulted in dispe rsed labelling along the chromosome arms, with a significant signal accumul ation in the pericentromeric region of all chromosomes. It is concluded tha t the pericentromeric heterochromatin of Z. biebersteiniana is composed of members of the Zbcen1 tandem repeat family and that these tandem arrays are intermingled with accumulated putative copia-like retrotransposon sequence s. An observed Rabl interphase orientation suggests that the length of the chromosomes rather than the genome size is the determining factor of the Ra bl phenomenon.