Heterochromatin and NORs variability inLeporinusfish (Anostomidae, Characiformes)

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Abstract
C-banding studies in four species of Characiformes fish of the genus Leporinus (Anostomidae) identified interspecific differences despite the strict similarity in karyotype macrostructure among them. A perceptible reduction in centromeric heterochromatin observed in L. piau seems to be a derived condition. L. amblyrhyncus and L. taeniatus exhibit a centromeric and telomeric heterochromatin pattern which is possibly basic in the group, and L. striatus shows a few exclusive intercalary blocks probably derived from inversions and/or transpositions. The nucleolar organizer regions, which were always found to be associated with heterochromatin segments, appear in different chromosomes or chromosome sites in the species studied, also indicating the occurrence of modifications during karyotype evolution in these fish.