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

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Fenocchio A. S., Bertolo L. A. C., Takahashi C. S., Camacho J. P. M.

Folia Biologica

2000

vol. 48

issue 3-4

105-109

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.

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

2003

vol. 51

issue 3-4

219-222

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.

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2 Folia Biologica

1 2003

1 2000

2 Fenocchio A. S.

1 Bertolo L. A. C.

1 Camacho J. P. M.

1 Cestari M. M.

1 Dias A. L.

1 Swarca A. C.

1 Takahashi C. S.

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

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