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Vol. 99, No. 1-4, 2002
Issue release date: 2002
Cytogenet Genome Res 99:164–169 (2002)

Chromosome evolution in fish: sex chromosome variability in Eigenmannia virescens (Gymnotiformes: Sternopygidae)

de Almeida-Toledo L.F. · Daniel-Silva M.F.Z. · Moysés C.B. · Fonteles S.B.A. · Lopes C.E. · Akama A. · Foresti F.
aDepartamento de Biologia, Instituto de Biociências, and bMuseu de Zoologia, Universidade de São Paulo, São Paulo; and cDepartamento de Morfologia, Instituto de Biociências, Universidade Estadual Paulista, Botucatu (Brazil).

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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.   

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