An XX/XY sex chromosome system in a fish species, Hoplias malabaricus, with a polymorphic NOR-bearing X chromosome.
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.
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Departamento de Ciências Morfo-Biológicas, FURG, RS, Brazil.
Bertollo
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D000818:Animals; D002871:Chromosome Banding; D004275:DNA, Ribosomal / Q000235:genetics; D005260:Female; D005399:Fishes / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence; D007621:Karyotyping; D008297:Male; D009697:Nucleolus Organizer Region; D012730:Sex Chromosomes; D012737:Sex Factors
D004275:DNA, Ribosomal