GENETIC DISTRIBUTION OF BARE-1-LIKE RETROTRANSPOSABLE ELEMENTS IN THEBARLEY GENOME REVEALED BY SEQUENCE-SPECIFIC AMPLIFICATION POLYMORPHISMS (S-SAP)

Retrotransposons are present in high copy number in many plant genomes . They show a considerable degree of sequence heterogeneity and insert ional polymorphism, both within and between species. We describe here a polymerase chain reaction (PCR)based method which exploits this poly morphism for the generation of molecular markers in barley. The method produces amplified fragments containing a Bare-1-like retrotransposon long terminal repeat (LTR) sequence at one end and a flanking host re striction site at the other. The level of polymorphism is higher than that revealed by amplified fragment length polymorphism (AFLP) in barl ey. Segregation data for 55 fragments, which were polymorphic in a dou bled haploid barley population, were analysed alongside an existing fr amework of some 400 other markers. The markers showed a widespread dis tribution over the seven linkage groups, which is consistent with the distribution of the Bare-1 class of retrotransposons in the barley gen ome based on in situ hybridisation data. The potential applicability o f this method to the mapping of other multicopy sequences in plants is discussed.