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Karyotype and nucleolar organizer regions of pygocentrus cariba (serraşalminae) from Caicara del Orinoco, Venezuela

Abstract:

Cytogenetic studies were conducted on Pygocentrus cariba from Caicara del Orinoco, Venezuela. The diploid chromosome number 2n=60 consisted of 18 metacentric, 30 submetacentric, 2 subtelocentric and 10 acrocentric chromosomes (NF = 110). A maximum of 12 nucleolar organizer regions (NOR) bearing chromosomes were visualized, with the NORs located terminally on the short arms of one pair of medium sized metacentric chromosomes, and on five small-sized acrocentric chromosome pairs. Constitutive heterochromatin blocks were located at centromeric and telomeric regions of practically all chromosomes, some being more conspicuous than others. Similarities between P. cariba and the species of the genus Serrasalmus 50 far studied, in terms of the number and type of chromosomes, multiplicity of NOR-bearing chromosomes and the distribution of constitutive heterochromatin located in centromeric and telomeric position, rein-forces the hypothesis of the close phylogenetic relationship between the genera Pygocentrus and Serrasalmus.