Use of meiotic FISH for identification of a new monosome in Gossypium hirsutum L.
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The extensive use of molecular cytogenetics in human genetics and clinical diagnostics indicates that analogous applications in plants are highly 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 tests with markers (cytogenetic, genetic, or molecular), which require sexual hybridization and at least one subsequent seed or plant generation. We have used meiotic fluorescence in situ hybridization (FISH) to analyze 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 A2-genome DNA revealed the monosome's D-subgenome origin. DAPI-PI staining showed that the monosome carries a major NOR, delimiting it to the major NOR-bearing chromosomes of the D-subgenome, i.e., 16 or 23. Dual-color FISH with 5S and 18S-28S rDNAs indicated that the monosome contains separate major clusters of each of these two tandemly repeated rDNA elements, thus delimiting the monosome to chromosome 23, for which the Cotton Cytogenetic Collection has previously been devoid of any sort of deficiency. Of the 26 chromosomes in the cotton genome, the Collection now provides coverage for 16 (70%) in the form of monosomy, and 20 (77%) in the form of monosomy and (or) telosomy. Use of molecular cytogenetic methods 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 methods, thus indicating their potential applicability to nearly all plant species.