Fluorescent in situ hybridization (FISH) of cloned probes provides a powerful tool for the integration of recombination, physical and cytogenetic maps. As part of a sorghum genomics project we have assigned the position of eight cloned DNA sequences to chromosome 1 of Sorghum bicolor . The probes used included a centromere-associated repeat, 28S-18S rDNA, a corn pollen-expressed Adh cDNA-selected sorghum bacterial artificial chromosome (BAC), and five RFLP-selected sorghum BACs. With the exception of the centromere-associated sequence and the 28S-18s rDNA, the probes produced FISH sites at the ends of the chromosome. The BACs selected from probes used to map two adjacent RFLP loci produced FISH signals at opposite ends of the chromosome. Over 85% of the physical length of this chromosome corresponded to approximately 12 map units separating the two RFLP loci. This indicates that most of the recombination and the loci of the ca. 120 cM RFLP map are located at the ends of the chromosome. Research supported by the Texas Advanced Technology and Research Program (grant 999902-090 to HJP and DMS), the Texas Agricultural Experiment Station, and the Texas A&M University Office of University Research.

Key words: chromosome 1, FISH, molecular cytogenetics, Sorghum bicolor