Chromosomal localization of the major ribosomal RNA genes in scallop Chlamys farreri

The chromosomes of Chlamys farreri were analyzed by means of silver staining and fluorescence in situ hybridization (FISH) with 18S-28S rDNA probe. Probe was made by PCR amplification of a DNA fragment containing internal transcribed spacers ITS1 between 18S and 5.8S ribosomal RNA gene, ITS2 between 5.8S and 28S ribosomal RNA gene and 5.8S rRNA gene, and labeled by PCR incorporation of bio-16-dUTP. FISH signals were located on the short arm of subtelocentric chromosome 10.After silverstaining, nucleolus organizer regions (NORs) could be observed on the telomere of the short arm of chromosome 10.However,one metaphase spread displayed an additional silver spot on the short arm of subtelocentric chromosome 12.