Untitled

Abstract

The chromosomes of Brachidontes rodriguezi were analysed by means of direct Giemsa staining, silver staining, fluorescent in-situ hybridization (FISH) with 18S + 28S rDNA probes, replication banding and chromomycin A3 (CMA) and DAPI fluorescence banding techniques. The diploid chromosome number in this species is 32 and the karyotype is composed of two pairs of metacentric chromosomes, 2 pairs of telo/subtelocentric chromosomes and 12 pairs of subtelocentric chromosomes. 18S + 28S rDNA clusters were located on the short arms of the two pairs of telo/subtelocentric chromosomes. The replication band pattern induced in this species facilitates chromosome pairing and differentiation. The nucleolar organizing regions (NORs) replicate late in the S phase and were associated with bright CMA fluorescence and dull DAPI fluorescence, but not all the four NORs showed bright CMA fluorescence in a given cell; intra- and interindividual variability was found for this character.

Cytogenetics of the razor clam <i>Solen marginatus</i> (Mollusca: Bivalvia: Solenidae)

“…To date chromosomes of five species of Mytilidae (Martí-nez- Lage et al, 1994Lage et al, , 1995Torreiro et al, 1999;Vitturi et al, 2000), one species of Donacidae (Martínez et al, 2002) and two species of Pharidae (Gonzá lez-Tizó n et al, in preparation) have been stained using CA 3 and DAPI fluorochromes. In S. marginatus the number of CA 3 bands varied from two to four; two of them are located subcentromerically in the long arms of the medium-sized subtelocentric pair 9 (Figs.…”

“…Fluorescence in situ hybridization using an 18S-5.8S-28S rDNA probe has been applied to 14 different species of bivalve: five Mytilidae Torreiro et al, 1999;Gonzá lez-Tizó n et al, 2000;Vitturi et al, 2000), two Ostreidae (Zhang et al, 1999;Xu et al, 2001), one Pectinidae , one Cardiidae (Insua et al, 1999), one Tellinidae (Gonzá lez-Tizó n et al, 2000), one Psammobiidae (Gonzá lezTizó n et al, 2000), one Donacidae (Martínez et al, 2002) and two Pharidae (Gonzá lez-Tizó n et al, in preparation). In all of these species most ribosomal loci locate at telomeric, and less frequently, at subtelomeric regions.…”

Karyotypic diversification in Mytilus mussels (Bivalvia: Mytilidae) inferred from chromosomal mapping of rRNA and histone gene clusters

“…NORs have been located in another six species of mytilids belonging to the genera Brachidontes [28-30], Perna [31], Perumytilus [32] and Xenostrobus [33]. These species show clear differences in the chromosomal distribution of the major rDNA clusters regarding both the number (one to four chromosome pairs) and morphology (metacentric to telocentric) of the NOR-bearing chromosome pairs, and in their chromosomal location (pericentromeric or subterminal to short or long arms), therefore indicating evolutionary changes in these clusters in Mytilidae.…”

A GC-rich satellite DNA and karyology of the bivalve mollusk <i>Donax trunculus:</i> a dominance of GC-rich heterochromatin

“…Concerning heterochromatin DNA composition, the C-banding technique does not give any indication about the GC-richness of the underlying tandemly arrayed satellite families. Although the GC content can be partially determined using basespecific fluorochromes, this method has been performed only in a few species of bivalves, and the chromosome complements of most of them reveal scarce GC-rich regions detectable by CMA staining (CMA-bright), located at only one to three chromosomal pairs and usually coincident with NORs (Martínez-Lage et al, 1995;Martínez-Expósito et al, 1997;Torreiro et al, 1999;Hurtado and Pasantes, 2005). Therefore, the detection of GC-rich interstitial bands on eight chromosome pairs in D. trunculus by indicates an unusual genome organization among bivalves.…”