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Cytogenetical and morphological considerations on Rhamdia quelen (Pisces, Pimelodidae) _ the occurrence of b chromosomes and polymorphic nor regions

Vera B.M. Hochberg; Bernardo Erdtmann

Departamento de Genética, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Caixa Postal 1953, 90001 Porto Alegre, RS, Brasil. Send correspondence to V.B.M.H.

ABSTRACT

Morphological and cytogenetic data are presented for two populations of Rhamdia quelen from Southern Brazil. Two modal chromosome numbers, 58 and 59, were detected due to the presence or absence of a supernumerary or B chromosome which is heterochromatic and resembles an isochromosome. Silver staining showed one pair of NOR-bearing chromosomes which may be polymorphic in relation to the size of the satellite regions and the secondary constriction. The presence of one pair of NOR seems to be the rule in the family Pimelodidae.

Keywords: cytogenetical; morphological; Rhamdia quelen ; b chromosomes; polymorphic.

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