Physical mapping of duplicated genomic regions of two chromosome ends in rice

Two genomic regions duplicated in distal ends of the short arms of chromoso mes 11 and 12 in rice (Oryza sativa L.) were characterized by YAC ordering with 46 genetic markers. Physical maps covering most of the duplicated regi ons were generated. Thirty-five markers, including 21 rice cDNA clones, sho wed the duplicated loci arrayed strictly in the same order along the two sp ecific genomic regions. Regardless of their different genetic distances, th e two duplicated segments may have a similar and minimum physical size with an expected length of about 2.5 Mb. However, differences of RFLP frequency for the duplicated DNA copies and recombination frequency for a given homo eologous area between the two regions were observed, indicating that these changes in genome organization occurred after the duplication. Our results establish a good model system for resolving the relationships between gene duplication, expression of duplicated genes, and the frequency of meiotic r ecombination in small chromosomal regions.