Dispersed repetitive DNA family members tend to be clustered in cotton. About 5000 plaques from a λ phage library of G. hirsutum(average insert size, 15 kb) were hybridized with each of seven different probes containing dispersed repeats. The seven families ranged from about 4,000 to 100,000 copies, spanning the full range of copy numbers for dispersed repeats discovered in cotton. The actual number of recombinant phages containing each repeat family was compared to the number that would be expected if individual family members were evenly distributed throughout the cotton genome. Each of the seven repeat families shows a high degree of clustering, as they are found on far fewer λ clones than would be expected if individual family members were evenly distributed throughout the genome. High-abundance families were found on as few as 1%–2% of the expected number of λ clones, a much greater degree of clustering than moderate-abundance families.
