title: A unique sex chromosome system in the knifefish Gymnotus bahianus with inferences about chromosomal evolution of Gymnotidae.
abstract: Cytogenetic studies in Neotropical electric knifefish of genus Gymnotus have shown a remarkable interspecific variability, including distinct sex chromosome systems. In this study, we present the first chromosomal data in Gymnotus bahianus from Contas River basin, northeastern South America. Based on extensive analyses, the modal diploid values were 2n = 36 (30m/sm + 6st) for females and 2n = 37 (32m/sm + 5st) for males. Therefore, a novel XX/XY1Y2 sex chromosome system is described for the genus. Single nucleolar organizer regions (NORs) interspersed to GC-rich sites were detected on a subtelocentric pair (7th) for both sexes and confirmed by ﬂuorescent in situ hybridization with 18S rDNA probes. Heterochromatin was detected at pericentromeric regions of all chromosomes and interspersed to NORs on pair 7 and 5S rDNA cistrons on pair 9. The highly differentiated karyotype of Gymnoytus bahianus, with low diploid numbers and a unique XX/XY1Y2 system, reinforces the independent origin of sex chromosomes in Gymnotiformes and seems to reflect the particular evolutionary history of this species in a small and isolated drainage system. Moreover, in spite of morphological similarities, the present results indicate a remarkable chromosomal divergence in relation to closely related species such as G. sylvius and G. carapo.
authors.affiliation: From the Universidade Estadual do Sudoeste da Bahia, Dep. Ciências Biológicas. Rua José Moreira Sobrinho, s/n. 45200-000 Jequié, BA, Brazil.
authors.forename: Josivanda S
authors.initials: JS
authors.lastname: Almeida
authors.affiliation: From the Universidade Estadual do Sudoeste da Bahia, Dep. Ciências Biológicas. Rua José Moreira Sobrinho, s/n. 45200-000 Jequié, BA, Brazil.
authors.forename: Vitor H
authors.initials: VH
authors.lastname: Migues
authors.affiliation: From the Universidade Estadual do Sudoeste da Bahia, Dep. Ciências Biológicas. Rua José Moreira Sobrinho, s/n. 45200-000 Jequié, BA, Brazil.
authors.forename: Débora
authors.initials: D
authors.lastname: Diniz
authors.affiliation: From the Universidade Estadual do Sudoeste da Bahia, Dep. Ciências Biológicas. Rua José Moreira Sobrinho, s/n. 45200-000 Jequié, BA, Brazil. paulomelloaffonso@yahoo.com.br.
authors.forename: Paulo Roberto A M
authors.initials: PR
authors.lastname: Affonso
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005260:Female; D023702:Gymnotiformes / Q000235:genetics*; D006570:Heterochromatin; D059785:Karyotype; D008297:Male; D009697:Nucleolus Organizer Region / Q000235:genetics; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D012730:Sex Chromosomes / Q000235:genetics*; D013020:South America
chemical_list: D006570:Heterochromatin; D012337:RNA, Ribosomal, 18S
keywords: Chromosomal evolution; FISH; Gymnotiformes; Neotropical fish; XX/XY1Y2