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) a
nd DAPI fluorescence banding techniques. The diploid chromosome number in t
his species is 32 and the karyotype is composed of two pairs of metacentric
chromosomes, 2 pairs of telo/subtelocentric chromosomes and 12 pairs of su
btelocentric 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 dif
ferentiation. The nucleolar organizing regions (NORs) replicate late in the
S phase and were associated with bright CMA fluorescence and dull DAPI flu
orescence, but not all the four NORs showed bright CMA fluorescence in a gi
ven cell; intra- and interindividual variability was found for this charact
er.