rDNA variants in S. lycopersicum genome. (A) Typical rDNA units in Sle0089P21 (18,122 bp). (B) Modified rDNA units found in BAC clone, HBa0007F24 (131,560 bp). There are seven variant repeats in the BAC clone. Retrotransposon sequences and extra-IGS regions are detected in 18S rRNA and 25S rRNA genes, respectively. Roman numerals in parentheses are the numbers of rDNA units in HBa0007F24. (C) More expanded IGS sequence in Sle0049A24 (28,040 bp).