ORGANIZATION OF REPETITIVE ELEMENTS IN THE UPLAND COTTON GENOME (GOSSYPIUM-HIRSUTUM)

To better understand the evolutionary nature of the economically important upland cotton (Gossypium hirsutum), 1,719 randomly chosen recombinants from a cosmid genomic library were examined for repetitive elements. Average insert size was approximately 34 kb, which represents 2.6% to 4.4% of the haploid genome of G. hirsutum (depending on the estimate for haploid genome size used). Probes representative of microsatellites, tandem repeats, transposable elements, a low copy number gene (catalase), and a chloroplast gene were used. Of the four dinucleotides, (CT)(n) and (GT)(n) were present in 3.6% and 1% of the clones, respectively, whereas, (AT)(n) hybridized to a single clone and (GC)(n), as well as the chloroplast gene, did not hybridize to any clone. The tandemly repeated rDNA cistron hybridized to 60 of the 1,719 clones. We estimate the copia-like family of retrotransposable element to be present in thousands of copies. When data from all probes are analyzed, the upland cotton genome consists of approximately 61% unique sequences and low copy number DNA, which agrees well with previously published estimates that were determined using other methods.