USE OF MEIOTIC FISH FOR IDENTIFICATION OF A NEW MONOSOME IN GOSSYPIUM-HIRSUTUM L

The extensive use of molecular cytogenetics in human genetics and clin ical diagnostics indicates that analogous applications in plants are h ighly feasible. One sort of application would be the identification of new aneuploids, which traditionally involves either direct karyotypic identification. which is feasible in only a few plant species, or tes ts with markers (cytogenetic, genetic, or molecular), which require se xual hybridization and at least one subsequent seed or plant generatio n. We have used meiotic fluorescence in situ hybridization (FISH) to a nalyze a new monosome of cotton (Gossypium hirsutum L., 2n=4x=52, 2(AD )(1)) that had a phenotype which seemed to be distinct from monosomes in the Cotton Cytogenetic Collection. Painting with A(2)-genome DNA re vealed the monosome's D-subgenome origin. DAPI-PI staining showed that the monosome carries a major NOR, delimiting it to the major NOR-bear ing chromosomes of the D-subgenome, i.e., 16 or 23. Dual-color FISH wi th 5S and 18S-28S rDNAs indicated that the monosome contains separate major clusters of each of these two tandemly repeated rDNA elements, t hus delimiting the monosome to chromosome 23, for which the Cotton Cyt ogenetic Collection has previously been devoid of any sort of deficien cy. Of the 26 chromosomes in the cotton genome, the Collection now pro vides coverage for 16 (70%) in the form of monosomy, and 20 (77%) in t he form of monosomy and (or) telosomy. Use of molecular cytogenetic me thods to identify a new plant aneuploid in cotton exemplifies the fact that a physicochemical karyotypic chromosome identification system is not required a priori for application of new molecular cytogenetic me thods, thus indicating their potential applicability to nearly all pla nt species.