Abstract The genomic organization and chromosomal distributions of two abundant tandemly repeated DNA sequences, dpTa1 and pSc119.2, were examined in six wild Hordeum taxa, representing the four basic genomes of the genus, by Southern and fluorescence in situ hy- bridization. The dpTa1 probe hybridized to between 30 and 60 sites on the chromosomes of all five diploid spe- cies studied, but hybridization patterns differed among the species. Hybridization of the pSc119.2 sequence to the chromosomes and Southern blots of digested DNA detected signals in Hordeum bulbosum, Hordeum chi- lense, Hordeum marinum and Hordeum murinum 4x, but not in Hordeum murinum 2x and Hordeum vulgare ssp. spontaneum. A maximum of one pSc119.2 signal was observed in the terminal or subterminal region of each chromosome arm in the species carrying this sequence. The species carrying the same I-genome differed in the presence (Hordeum bulbosum) or absence (Hordeum spontaneum) of pSc119.2. The presence of pSc119.2 in the tetraploid cytotype of Hordeum murinum, but its ab- sence in the diploid cytotype, suggests that the tetraploid is not likely to be a simple autotetraploid of the diploid. Data about the inter- and intra-specific variation of the two independent repetitive DNA sequences give infor- mation about both the interrelationships of the species and the evolution of the repetitive sequences. Key words Barley · Hordeum · In situ hybridization · Phylogeny · Tandemly repeated DNA sequence Introduction Genes show extensive conservation over wide taxonomic distances so that, at the DNA level, homologous coding sequences can be isolated from many species in a taxo- nomic grouping (e.g. in the grasses, Sasaki 1996). In contrast, the single-copy sequences flanking many stretches of simple sequence repeats (microsatellites) are often species-specific and, within the Triticeae, the great majority of such markers are unique to one genome (Waugh et al., personal communication). Repetitive DNA sequences – DNA motifs that are repeated hun- dreds or thousands of times in the genome – make up the majority of most plant genomes and examples both with a widespread distribution and with high species (or ge- nome) specificity have been reported (see Schmidt and Heslop-Harrison 1998). As well as genome-specific dispersed and localized sequences, many sequences with a more-widespread ge- nome distribution have been isolated. These are of value for studying the occurrence and mechanisms of both se- quence and species evolution. Tandemly repeated se- quences have been isolated and characterized from the Triticeae, and are investigated here in the genus Horde- um. pSc119.2 was among the first tandemly repeated DNA sequences to be isolated from cereals (Bedbrook et al. 1980), representing several percent of the rye ge- nome. (It was originally cloned as a chimera which was separated by McIntyre et al. 1990.) Sequences homolo- gous to this 118-bp repeat have been found widely in the Triticeae, and even outside (Katsiotis et al. 1997, in Avena), but notably Southern and in situ hybridization cannot detect its presence in Hordeum vulgare, although it is present in many other Hordeum species (Gupta et al. 1989). Vershinin et al. (1996) were able to show its pres- ence by PCR analysis in low copy number in Hordeum vulgare and showed details of its higher-order structure in rye (Vershinin et al. 1995;Vershinin and Heslop-Harri- son 1998). Another subtelomeric tandemly repeated se- quence (the HvRT family sequence) also shows a charac- teristic, but different, species-specific distribution among Communicated by P. Langridge S. Taketa ( ✉ ) · H. Ando · K. Takeda Research Institute for Bioresources, Okayama University, Chuo 2–20–1, Kurashiki 710–0046, Japan G.E. Harrison · J.S. Heslop-Harrison Department of Cell Biology, John Innes Centre, UK Present address: S. Taketa, Faculty of Agriculture, Kagawa Univeristy, Miki-cho, Kita-gun, Kagawa 761–0795, Japan e-mail: staketa@ag.kagawa-u.ac.jp Fax: 81 87 891 3021 Theor Appl Genet (2000) 100:169–176 © Springer-Verlag 2000 ORIGINAL PAPER S. Taketa · H. Ando · K. Takeda · G. E. Harrison J. S. Heslop-Harrison The distribution, organization and evolution of two abundant and widespread repetitive DNA sequences in the genus Hordeum Received: 17 March 1999 / Accepted: 16 June 1999