title: Repetitive DNA and meiotic behavior of sex chromosomes in Gymnotus pantanal (Gymnotiformes, Gymnotidae).
abstract: Neotropical fishes have a low rate of chromosome differentiation between sexes. The present study characterizes the first meiotic analysis of sex chromosomes in the order Gymnotiformes. Gymnotus pantanal - females had 40 chromosomes (14m/sm, 26st/a) and males had 39 chromosomes (15m/sm, 24st/a), with a fundamental number of 54 - showed a multiple sexual determination chromosome system of the type X(1)X(1)X(2)X(2)/X(1)X(2)Y. The heterochromatin is restricted to centromeres of all chromosomes of the karyotype. The meiotic behavior of sex chromosomes involved in this system in males is from a trivalent totally pared in the pachytene stage, with a high degree of similarity. The cells of metaphase II exhibit 19 and 20 chromosomes, normal disjunction of sex chromosomes and the formation of balanced gametes with 18 + Y and 18 + X(1)X(2) chromosomes, respectively. The small amount of heterochromatin and repetitive DNA involved in this system and the high degree of chromosome similarity indicated a recent origin of the X(1)X(1)X(2)X(2)/X(1)X(2)Y system in G. pantanal and suggests the existence of a simple ancestral system with morphologically undifferentiated chromosomes.
authors.affiliation: Programa de Pós-Graduação em Biologia Evolutiva, Universidade Estadual de Ponta Grossa, Ponta Grossa, Brazil.
authors.forename: M
authors.initials: M
authors.lastname: da Silva
authors.forename: D A
authors.initials: DA
authors.lastname: Matoso
authors.forename: M R
authors.initials: MR
authors.lastname: Vicari
authors.forename: M C
authors.initials: MC
authors.lastname: de Almeida
authors.forename: V P
authors.initials: VP
authors.lastname: Margarido
authors.forename: R F
authors.initials: RF
authors.lastname: Artoni
mesh_terms: D000818:Animals; D001483:Base Sequence; D002871:Chromosome Banding; D005260:Female; D023702:Gymnotiformes / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence; D059785:Karyotype; D007621:Karyotyping; D008297:Male; D008540:Meiosis / Q000235:genetics*; D008969:Molecular Sequence Data; D049471:Pachytene Stage / Q000235:genetics; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics*; D017422:Sequence Analysis, DNA; D012730:Sex Chromosomes / Q000235:genetics*