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1

Analyses of the structure of NORs in two species of south American Sorubiminae fishes (Siluriformes) by means of several cytogenetic techniques

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Swarca A. C., Fenocchio A. S., Cestari M. M., Dias A. L.
Folia Biologica
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2008
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vol. 56
|
issue 1-2
31-35
EN
Several cytogenetic techniques (AgNOR, C- G- and RE bandings, DAPI, CMA3 and FISH) were applied in order to analyze the structure and variability of NORs in the fish species Steindachneridion melanodermatum and S. scripta. Ag-NORs were observed on the short arm of the first acrocentric chromosome pair, coincidentally with a strong C-positive band on a large secondary constriction. In addition, NORs showed bright fluorescent signals when stained with CMA3 and treated for FISH with rDNA 18S. However, they showed negative coloration after G- and restriction enzyme banding and DAPI staining. The results evidence a substantial size polymorphism in these regions. The NOR bearing chromosomes in both species may be considered homologues because they maintain conserved characteristics, such as being interspersed with a GC-rich heterochromatin and possessing target sequences for AluI, BamHI and EcoRI.
2

Karyotypic characterization and NOR analysis by different banding techniques of Rhamdia quelen from the first plateau of the Iguacu River (Brazil)

100%
Fenocchio A. S., Swarca A. C., Cestari M. M., Dias A. L.
Folia Biologica
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2003
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vol. 51
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issue 3-4
219-222
EN
A population of R. quelen from the first plateau of the Iguacu River (Parana State, Brazil) was analyzed cytogenetically. A diploid set of 58 chromosomes was constituted by 32 M, 16 SM, 6 ST and 4 A (FN=116). In one individual a 2n=59 karyotype was determined due to the presence of one additional metacentric heterochromatic chromosome. NORs, detected by AgNO3 and CMA3 staining as well as fluorescence in situ hybridization with an 18S rDNA probe, are located at a terminal position on the short arms of a ST chromosome pair. C-banding marks the NORs and other weak bands distributed on telomeric regions of some chromosomes. These results give evidence that Rhamdia constitute, in terms of karyotypic macrostructure, a conserved group and support the idea that several synonymous species may be included in this genus.
3

B chromosomes in two fish species genus Rhamdia (Siluriformes, Pimelodidae)

100%
Fenocchio A. S., Bertolo L. A. C., Takahashi C. S., Camacho J. P. M.
Folia Biologica
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2000
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vol. 48
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issue 3-4
105-109
EN
Specimens belonging to two fish species genus Rhamdia were cytogenetically analysed from seven localities in Brazil and Argentina. In addition to the 58 chromosomes of the basic karyotype, one to five metacentric B chromosomes were observed carrying conspicuous heterochromatic blocks on the distal regions of both chromosome arms. These B chromosomes are mitotically stable and, in the two best-sampled populations in R. hilarii (Lobo and 29 reservoirs), they showed frequency distributions fitting a binomial distribution, though Bs were more frequent in the latter. The presence of B chromosomes with the same appearance in R. quelen suggests an ancient origin for these B chromosomes, presumably prior to speciation from a common ancestor.
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