CLONING AND CHARACTERIZATION OF THE MAJORITY OF REPETITIVE DNA IN COTTON (GOSSYPIUM L)

Repetitive DNA elements representing 60-70% of the total repetitive DN A in tetraploid cotton (Gossypium barbadense L.) and comprising 30-36% of the tetraploid cotton genome were isolated from a genomic library of DNA digested with a mixture of four blunt-end cutting restriction e nzymes. A total of 313 clones putatively containing nuclear repetitive sequences were classified into 103 families, based on cross hybridiza tion and Southern blot analysis. The 103 families were characterized i n terms of genome organization, methylation pattern, abundance, and DN A variation. As in many other eukaryotic genomes, interspersed repetit ive elements are the most abundant class of repetitive DNA in the cott on genome. Paucity of tandem repeat families with high copy numbers (> 10(4)) may be a unique feature of the cotton genome as compared with o ther higher plant genomes. Interspersed repeats tend to be methylated, while tandem repeats seem to be largely unmethylated in the cotton ge nome. Minimal variation in repertoire and overall copy number of repet itive DNA elements among different tetraploid cotton species is consis tent with the hypothesis of a relatively recent origin of tetraploid c ottons.