Chromosome marker of T. trichopterus Cytogenetic study
of T. Trichopterus performed by Ag-NOR staining
technique is the first report. The objective of this
technique is to detect for nucleolar organizer regions
(NORs) which represent the location of genes that
function in ribosome synthesis (18S and 28S ribosomal
RNA). NORs produce numerous gene expressions and it
composes of non-histone protein more than others chromosome
regions. So, the specific dark band is induced by
the reduction of organic silver by these proteins that
change silver to be dark [6]. The region adjacent to the
telomere of chromosome pair 2 showed clearly observable
secondary constriction (nucleolar organizer regions,
NORs). As such, the extra characteristic of chromosome
pair 2 is the representative of chromosome marker. Over
200 species of fishes have been investigated by Ag-NOR
staining technique, some of which have been applied to
elucidate taxonomic and morphological affinities, e.g. in
family Cyprinidae [5]. Moreover, the amount and location
of NOR can explain the evolution of each chromosome.
Normally, most fishes have only 1 pair of small NORs in a
chromosome complement. If some fish has more than 2
NORs, it may have caused by translocation between NOR
containing and another chromosome. Furthermore, NOR
usually locate close to telomere of chromosome arm. If
NOR appears between centromere and telomere, it may be
caused by the centric fusion or pericentric inversion
between 2 telocentric chromosomes that one chromosome
has NOR at telomere according to the case study of
spotted snakehead (Channa punctata) in family Channidae
[13].