RESUMO
A comparison of R-banding patterns obtained by 5-bromodeoxyuridine incorporation was made between the chromosomes of two fish species of the genus Astyanax (Characiformes: Tetragonopterinae), A. altiparanae with 2n = 50 chromosomes, and A. schubarti with 2n = 36 chromosomes. The two species present the highest and the lowest chromosome numbers found in this fish genus, respectively, for which the modal chromosome number is 50. R-band homeology was detected, involving eleven chromosomes of A. schubarti and seventeen chromosomes of A. altiparanae, indicating a close chromosomal relationship between the two species, in spite of their great difference in chromosome number. A chromosome fusion in the past history of the group was hypothesized as a possible cause of the discrepant chromosome numbers of the two species.
Assuntos
Bromodesoxiuridina/química , Cromossomos/química , Cromossomos/genética , Evolução Molecular , Peixes/genética , Animais , Brasil , Bandeamento Cromossômico/métodos , Análise Citogenética/métodos , Feminino , Genética Populacional/métodos , Masculino , Mitose/genética , Rios , Homologia de Sequência do Ácido Nucleico , Especificidade da EspécieRESUMO
Major and 5S ribosomal genes have been localized in chromosomes from five fish species, genus Astyanax, using in situ hybridization (FISH) with 28S and 5S rDNA probes. In situ signals for the major rDNA co-localized with the 5S rDNA clusters in the pericentromeric region of one marker chromosome in all five species analyzed. The conserved localization of these two rDNA clusters in the five related Astyanax species was considered as indicative of a close relationship among them. The use of these molecular markers for elucidating evolutionary relationships among closely related taxa is discussed.
Assuntos
Mapeamento Cromossômico , DNA Ribossômico/genética , Peixes/genética , RNA Ribossômico 5S/genética , Animais , Sequência de Bases , Primers do DNA , Hibridização in Situ Fluorescente , Reação em Cadeia da PolimeraseRESUMO
New data are presented on the sex chromosomes of the fish species Eigenmannia virescens (Gymnotiformes, Sternopygidae). A new finding, involving the occurrence of ZZ/ZW sex chromosomes, is described in specimens sampled from the São Francisco and Amazon river basins in Brazil. All individuals had a chromosome number of 2n = 38. The homologs of the sex chromosome pair from the São Francisco river basin sample differed only in their morphology, while those from the Amazonian sample differed both in morphology and heterochromatin pattern. A possible model for the evolution of the sex chromosomes in E. virescens is proposed, including data from populations from the Paraná (Brazil) river basin, in which male heterogamety has already been described. The occurrence of different sex chromosome systems in species and populations of the neotropical freshwater fish fauna is discussed.