title: First Cytogenetic Description of Microsternarchus bilineatus (Gymnotiformes: Hypopomidae) from Negro River (Brazilian Amazon).
abstract: Microsternarchus bilineatus is a neotropical electric fish species widely distributed in Amazonian ecosystems. This work reports the first karyotypic description of the species M. bilineatus, which presented 2n = 48 chromosomes, with a distinct karyotypic formula between the sexes: males with 21 metacentric (m)/submetacentric (sm) + 27 subtelocentric (st)/acrocentric (a) and fundamental number (FN) = 69 and females with 20 m/sm + 28 st/a and FN = 68. We found a probable recent sex system of XX/XY type. The nucleoli organizer regions (NORs) were multiple terminally located, and the heterochromatic blocks were mostly pericentromeric. The 18S rDNA markings confirmed NORs and their distinction between sexes, which suggested some differential role of this gene related to gender in this species. The 5S rDNA presented terminal markings on a single chromosome pair, with no distinction between sexes, and the telomeric probes have shown a uniform pattern in males and females.
authors.affiliation: 1 Laboratório de Fisiologia Comportamental e Evolução, Coordenação de Biodiversidade, Instituto Nacional de Pesquisas da Amazônia-INPA , Manaus, Brazil .
authors.forename: Isac Silva
authors.initials: IS
authors.lastname: de Jesus
authors.affiliation: 2 Laboratório de Genética Animal, Coordenação de Biodiversidade, Instituto Nacional de Pesquisas da Amazônia , Manaus, Brazil .
authors.forename: Milena
authors.initials: M
authors.lastname: Ferreira
authors.affiliation: 3 Laboratório de Citogenética, Departamento de Ciências Biológicas, Universidade Estadual do Sudoeste da Bahia , Jequié, Brazil .
authors.forename: Caroline
authors.initials: C
authors.lastname: Garcia
authors.affiliation: 2 Laboratório de Genética Animal, Coordenação de Biodiversidade, Instituto Nacional de Pesquisas da Amazônia , Manaus, Brazil .
authors.forename: Leila Braga
authors.initials: LB
authors.lastname: Ribeiro
authors.affiliation: 1 Laboratório de Fisiologia Comportamental e Evolução, Coordenação de Biodiversidade, Instituto Nacional de Pesquisas da Amazônia-INPA , Manaus, Brazil .
authors.forename: José Antônio
authors.initials: JA
authors.lastname: Alves-Gomes
authors.affiliation: 2 Laboratório de Genética Animal, Coordenação de Biodiversidade, Instituto Nacional de Pesquisas da Amazônia , Manaus, Brazil .
authors.forename: Eliana
authors.initials: E
authors.lastname: Feldberg
mesh_terms: D000818:Animals; D001938:Brazil; D005260:Female; D023702:Gymnotiformes / Q000235:genetics*; D059785:Karyotype; D008297:Male; D009697:Nucleolus Organizer Region; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D012341:RNA, Ribosomal, 5S / Q000235:genetics; D012727:Sex Characteristics; D012730:Sex Chromosomes / Q000235:genetics*
chemical_list: D012337:RNA, Ribosomal, 18S; D012341:RNA, Ribosomal, 5S
keywords: electric fish; freshwater; neotropics; sex chromosomes