rDNA (18S-28S and 5S) co-localization and linkage between ribosomal genes and (TTAGGG)n telomeric sequence in the earthworm Octodrilus complanatus (Annelida: Oligochaeta: Lumbricidae) revealed by single- and double-colour FISH

Spermatogonial and metaphase I chromosomes of the lumbricid earthworm Octodrilus complanatus (Annelida: Oligochaeta) were examined using fluorescent in situ hybridization (FISH) with three repetitive DNA probes—5S rDNA, 18S–26S rDNA, and (TTAGGG)n. Single-color FISH consistently mapped one chromosome pair per spread using either 5S rDNA or 18S–26S rDNA as probes. Simultaneous (18S–26S)-5S and (18S–26S)-(TTAGGG)nFISH demonstrated that repeated units of the two ribosomal families were overlapped and closely associated with telomeric sequences.