A physical map with yeast artificial chromosome (YAC) clones covering 63% of the 12 rice chromosomes

A new YAC (yeast artificial chromosome) physical map of the 12 rice chromos omes was constructed utilizing the latest molecular linkage map. The 1439 D NA markers on the rice genetic map selected a total of 1892 YACs from a YAC library. A total of 675 distinct YACs were assigned to specific chromosoma l locations. In all chromosomes, 297 YAC contigs and 142 YAC islands were f ormed. The total physical length of these contigs and islands was estimated to 270 Mb which corresponds to approximately 63% of the entire rice genome (430 Mb). Because the physical length of each YAC contig has been measured , we could then estimate the physical distance between genetic markers more precisely than previously. In the course of constructing the new physical map, the DNA markers mapped at 0.0-cM intervals were ordered accurately and the presence of potentially duplicated regions among the chromosomes was d etected. The physical map combined with the genetic map will form the basis for elucidation of the rice genome structure, map-based cloning of agronom ically important genes, and genome sequencing.