DETAILED COMPARATIVE MAPPING OF CEREAL CHROMOSOME REGIONS CORRESPONDING TO THE PH1 LOCUS IN WHEAT

Detailed physical mapping of markers from rice chromosome 9, and from syntenous (at the genetic level) regions of other cereal genomes, has resulted in rice yeast artificial chromosome (YAC) contigs spanning pa rts of rice 9. This physical mapping, together with comparative geneti c mapping, has demonstrated that synteny has been largely maintained b etween the genomes of several cereals at the level of contiged YACs. M arkers located in one region of rice chromosome 9 encompassed by the Y AC contigs have exhibited restriction fragment length polymorphism (RF LP) using deletion lines for the Phl locus. This has allowed demarcati on of the region of rice chromosome 9 syntenous with the ph1b and ph1c deletions in wheat chromosome 5B. A group of probes located in wheat homoeologous group 5 and barley chromosome 5H, however, have synteny w ith rice chromosomes other than 9. This suggests that the usefulness o f comparative trait analysis and of the rice genome as a tool to facil itate gene isolation will differ from one region to the next, and impl ies that the rice genome is more ancestral in structure than those of the Triticeae.