ANALYSIS OF THE BARLEY AND RICE GENOMES BY COMPARATIVE RFLP LINKAGE MAPPING

Comparative genetic mapping of rice and barley, both major crop specie s with extensive genetic resources, offers the possibility of uniting two well-established and characterized genetic systems. In the present study, we screened 229 molecular markers and utilized 110 polymorphic orthologous loci to construct comparative maps of the rice and barley genomes. While extensive chromosomal rearrangements, including invers ions and intrachromosomal translocations, differentiate the rice and b arley genomes, several syntenous chromosomes are evident. Indeed, seve ral chromosomes and chromosome arms appear to share nearly identical g ene content and gene order. Seventeen regions of conserved organizatio n were detected, spanning 287 cM (24%) and 321 cM (31%) of the rice an d barley genomes, respectively. The results also indicate that most (7 2%) of the single-copy sequences in barley are also single copy in ric e, suggesting that the large barley genome arose by unequal crossing o ver and amplification of repetitive DNA sequences and not by the dupli cation of single-copy sequences. Combining these results with those pr eviously reported for comparative analyses of rice and wheat identifie d nine putatively syntenous chromosomes among barley, wheat and rice. The high degree of gene-order conservation as detected by comparative mapping has astonishing implications for interpreting genetic informat ion among species and for elucidating chromosome evolution and speciat ion.