MOLECULAR CYTOGENETIC CHARACTERIZATION OF THE TERMINAL HETEROCHROMATIC SEGMENT OF THE B-CHROMOSOME OF RYE (SECALE-CEREALE)

The terminal heterochromatic segments of the long arms of 20 rye B-chr omosomes were isolated by means of laser microdissection technology. A lso the remaining portions of the long arms, along with the short arms of the same chromosomes were isolated. Each sample was used for degen erate oligonucleotide primer-polymerase chain reaction (DOP-PCR) ampli fication reactions. The resulting products were used as probes for chr omosome in situ hybridisation experiments, and in Southern hybridisati on to digests of OB and +B DNA. Competition hybridisation of these pro bes with OB DNA allowed the detection of B-specific sequences. The ter minal heterochromatin of the rye B-chromosome contains both B-specific sequences and sequences also present on the A-chromosomes of rye. The B-specific D1100 family is the major repeat species located in the te rminal heterochromatin. Primers designed to the cloned sequence (E1100 ) were used to search for related low copy sequences in OB DNA. The se quences of the PCR products revealed no similarities to that of the cl one E1100 except for the primer sequences. The possible origin of this sequence is discussed in the context of models for the evolution of t he rye B-chromosome.