This work provides the first detailed report on diploid number, karyotype formula, distribution of constitutive heterochromatin and nucleolus organizing regions (NORs) in Sparisoma chrysopterum (Bloch & Schneider 1801). The species has a modal diploid number 2n = 46 chromosomes composed of 8 metacentric (m), 10 submetacentric (sm), 10 subtelocentric (st) and 18 acrocentric (a) elements and a number of arms (NF) equal to 74. C-banding revealed a nonhomogeneous distribution of constitutive heterochromatin occupying pericentromeric sites on nearly all chromosomes but with terminal blocks on the long arm in the metacentric series, whereas the submetacentric series terminal exhibited blocks located preferentially on the short arms. Three pairs of chromosomes presented weak staining for heterochromatic areas. Silver nitrate impregnation revealed a single pair of NORs located in the terminal position of the short arms of chromosome pair No. 12, and their variation among Sparisoma species seems to indicate that it is an important chromosomal marker in the genus. The data presented here confirm that Scaridae have a conserved diploid number (46-48) with notable karyotypic variation and support that the occurrence of numerous pericentric inversion events could be responsible for modifying the karyotypic formula and that microstructural alterations, likely translocations, involving NORs have frequently occurred during diversification into the genus Sparisoma.
