In situ hybridization of biotinylated DNA probes to cotton meiotic chromosomes

A modified procedure for in situ hybridization of biotinylated probes to meiotic chromosomes of cotton has been developed with high retention of squashed cells on slides, preservation of acid-fixed chromosome morphology, exceptionally low levels of background precipitate at nonspecific hybridization sites and improved photomicrographic recording. Salient features of the techniques include pretreatment of slides before squashing, cold storage of squash preparations, and use of interference filters for distinguishing precipitate from chromatin. A cloned 18S/28S ribosomal DNA fragment from soybean was biotinylated via nick-translation and hybridized to microsporocyte meiotic chromosomes of cotton (Gossypium hirsutum L. and G. hirsutum L. X G. barbadense L.). Enzymatically formed precipitate from streptavidin-bound peroxidase marked the in situ hybridization. In situ hybridization of biotinylated probes to cotton meiotic chromosomes adds the specificity and resoltion of in situ hybridization to the chromosomal and genomic perspectives provided by meiotic cytogenetic analyses. Molecular cytogenetic analyses of meiotic cells offer certain inherent analytical advantages over analyses of somatic cells, e.g., in terms of mapping, and for studying fundamental biological and genetic problems, particularly for organisms that are not amenable to somatic karyotypic analysis.