Chromosome analysis and mapping of ribosomal genes by one- and two-color fluorescent in situ hybridization in Hinnites distortus (Bivalvia: Pectinidae).

Metaphase chromosomes of the scallop Hinnites distortus were analyzed using Giemsa staining, chromosome measurements, silver staining, one- and two-color fluorescent in situ hybridization (FISH) ribosomal DNA (rDNA) probes, and 4',6-diamidino-2-phenylindole (DAPI) banding compatible with in situ hybridization. The karyotype (2n = 38) consists of three submetacentric-metacentric, one submetacentric, one subtelocentric-submetacentric, and 14 subtelocentric pairs. The 18S-28S rDNA maps at the centromeric level of two subtelocentric pairs, but not more than two nucleolus organizer region (NOR)-bearing chromosomes were transcriptionally active. The 5S rDNA seems to show a conventional tandem arrangement with a repeat unit of about 450 bp and it maps at the pericentromeric region of the long arm of one subtelocentric pair. Two-color FISH demonstrated that 18S-28S rDNA and 5S rDNA are not syntenic. Sequential FISH/Giemsa staining and subsequent chromosome pairing allow us to propose that pairs 9 and 12 carry the 18S-28S rDNA and pair 13 carries the 5S rDNA. All chromosomes are characterized as containing constitutive heterochromatin at the centromeric region. The data provided are the first contribution toward construction of the molecular karyotype of H. distortus and will be useful in assessing evolutionary relationships within scallops.

Identification of four scallop species using PCR and restriction analysis of the ribosomal DNA internal transcribed spacer region.

Polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis of the ribosomal DNA region spanning the 5.8S RNA gene and the 2 flanking internal transcribed spacers (ITSs) was performed to establish DNA-based molecular markers for the identification of the scallops Aequipecten opercularis, Chlamys distorta, Mimachlamys varia, and Pecten maximus. Chlamys distorta was distinguished simply by ITS size. Species-specific restriction patterns were found with the restriction enzyme AluI, and also with SmaI for A. opercularis and M. varia. When ITS sizes and the RFLPs obtained with SmaI were combined, the 4 scallops were also differentiated. Additional species-specific RFLPs were revealed after ITS-2 PCR amplification and subsequent digestion with Hsp92II. Using this marker, canned scallops were identified. Thus this work provides a simple, reliable, and rapid method for the identification of scallops that can be used when species-specific morphologic characteristics are removed or when specimens are small in size.

Characterization of Aequipecten opercularis (Bivalvia: Pectinidae) chromosomes by different staining techniques and fluorescent in situ hybridization.

The chromosomes of the queen scallop Aequipecten opercularis were studied using conventional Giemsa staining, chromosome measurements, C-banding, silver staining, and fluorescent in situ hybridization (FISH) with 18S-28S rDNA and 5S rDNA probes. The karyotype (2n = 26) consists of large metacentric (pairs 1 and 2), telocentric (pairs 3, 4, 5, 6, 7, 8, and 9), and small metacentric chromosomes (pairs 10, 11, 12, and 13). The C-bands observed can be described as major and minor C-bands which are differentiated according to the intensity of the fluorescence and the frequency of the detection. Major C-bands were found on the long arm of the chromosome pairs 6, 7, 8, and 9 in an intercalary or subterminal position. Minor C-bands were located in the centromeric region in all chromosomes of the complement and also on one arm of pairs 12 and 13 in a terminal position. Silver spots were detected on the telomere of the long arms of one or two chromosomes of pair 7 in every case, although in two individuals up to four additional silver spots were detected. These were located on pairs 8 and 9 in the same position as the C-bands. 18S-28S ribosomal genes were found by FISH on the long arm of chromosome pair 7.5S ribosomal genes were located subterminally on one arm of metacentric pair 1, but two sites were differentiated in the case of elongated chromosomes. The results obtained allow for the identification of at least six different chromosome pairs in A. opercularis and contribute to the construction of an idiogram that is suitable for gene mapping and establishing accurate interspecific comparisons in scallops.