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Nucleolar organizing regions, 18S and 5S rDNA in Astyanax scabripinnis (Pisces, Characidae): populations distribution
D A Ferro1, D M Néo, O Moreira-Filho
1Universidade Federal de São Carlos, Departamento de Genética e Evolução, SP, Brazil.
Abstract:
Astyanax scabripinnis specimens from four distinct populations in Brazil were studied with respect to their karyotype macrostructure, nucleolar organizer regions, and 18S and 5S rRNA genes. The four populations showed a 2n = 50 chromosomes (3 M + 11 SM + 5 ST + 6 A pairs) and 1-2 B chromosomes. No chromosomal differentiations were observed between sexes. Although a karyotypic diversity has been characterized in this fish group, the populations now analyzed presented the same macrokaryotypic pattern. Chromosome mapping of 5S rDNA showed a total of eight sites located in four distinct chromosomal pairs, with no apparent differences among populations. A comparative study on 18S rDNA locations and Ag-NORs showed some secondary NOR sites that are not usually expressed in karyotypes and a probable differential NOR activity among populations. Correlations between these data, environmental conditions and B chromosomes are discussed.
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