Fig. 1 Generalized ribosomal DNA unit structure and rDNA restriction site map of Gossypium hirsutum cv. TM1. The positions of the 12 restriction enzyme sites are indicated. The location of the two rice probes pRY12 and pRY18 is shown. The enzymes used are: X, XbaI; B, BamHI; Nc, NcoI; Sp, SpeI; E, EcoRI; S, SacI; Ev, EcoRV; Be, BstEII; D, DraI; Ns, NsiI; Ss, SspI; and Bg, BglI