Chromosome Research

, Volume 8, Issue 2, pp 111–118 | Cite as

An XX/XY Sex Chromosome System in a Fish Species, Hoplias malabaricus, with a Polymorphic NOR-Bearing X Chromosome

  • Guassenir Gonçalves Born
  • Luiz Antonio Carlos Bertollo


Cytogenetic studies were carried out in the fish, Hoplias malabaricus, from the Parque Florestal do Rio Doce (Brazil). This population is characterized by 2n = 42 chromosomes for both males and females and an XX/XY sex chromosome system, confirmed through several banding methods. Females show 24 metacentric, 16 submetacentric and 2 subtelocentric chromosomes. Males show 24 metacentric, 17 submetacentric and 1 subtelocentric chromosomes. While the X chromosome is easily recognized (the only subtelocentric element), the Y chromosome is somewhat difficult to identify but appears to correspond to the smallest submetacentric in the male karyotype. In-situ hybridization with an 18S rDNA probe showed 10 well-labeled chromosomes, including the X chromosome. The 5S rDNA is interstitially located in a single metacentric pair independent of the 18S rDNA sites. The NOR on the X chromosome is always active and occurs adjacent to a heterochromatic distal segment on the long arm. Variations in size of the NORs and/or heterochromatic segment correspond to a polymorphic size condition observed in the X chromosome. The present results confirm the XX/XY sex chromosome system in the population analyzed as well as a new cytotype in the Hoplias malabaricus group.

Hoplias malabaricus polymorphic NOR 5S rDNA 18S rDNA sex chromosomes 


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Copyright information

© Kluwer Academic Publishers 2000

Authors and Affiliations

  • Guassenir Gonçalves Born
    • 1
  • Luiz Antonio Carlos Bertollo
    • 2
  1. 1.Departamento de Ciências Morfo-BiológicasFURG, RSBrazil
  2. 2.Departamento de Genética e EvoluçboUniversidade Federal de São CarlosSbo Carlos, SPBrazil

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