Plant Genome III Conference Plant Genome III Conference
Cytogenetics has played a very minor role in the recent soybean genetic advances due the small size, relatively large number and morphological homogeneity of its chromosomes. We have taken advantage of the major advances in soybean molecular genetic mapping and coupled it to new cytogenetic analyses to develop the molecular cytogenetics of soybean. High signal FISH cytogenetic markers have been developed from 1) two highly repeated soybean satellite families, 2) the 5S and 45S rDNA loci, and 3) lowcopy YAC clones. It has been possible to identify probes that are chromosome specific or, at least, restricted to a small subset of chromosomes. Segregation analysis has identified genetic map positions for some of the high-intensity markers, but joining the developing cytogenetic map with the genetic map may be better accomplished using previously mapped RFLP or PCR-based genetic markers. We have succeeded in detecting several small (2 to 8 kbp) RFLP tagged sites with FISH and even smaller PCR-tagged sites (<1 kbp) using in situ PCR. In all, particular cytogenetic markers are now known to reside on genetic linkage groups H, K, L, P and J. A comprehensive and widely applied cytogenetic map will provide complementary information to the growing genetic mapping database and help answer evolutionary questions that cannot be readily approached by segregation analysis. Indeed, cytogenetics can enhance map- based cloning strategies by providing sub-genomic libraries for isolating particular sequences. We are currently attempting specific chromosome isolation using microscopic manipulation.