Cytogenetic studies in gomphocerine grasshoppers. II. Chromosomal location of active nucleolar organizing regions

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Abstract
Nucleolar organizing region (NOR) location has been studied in 20 species of gomphocerine grasshoppers. In the 17 species with 2n (♀) = 17, the largest number carry an active NOR on the L2, L3, and X chromosomes. The M4, M5, M6, and S8 show NOR activity in some species, but the L1 and M7 do not carry a NOR in any. While almost all NORs on L2, L3, and X show primary activity, a majority of these on the M4, M5, M6, and S8 are secondary and express a nucleolus only in a minority of male meiocytes. The NORs are located preferentially at particular chromosomal sites; primary active NORs prevail in interstitial locations, while secondary active NORs predominate in paracentromeric locations. In the majority of the species analyzed in this report, primary and secondary active NORs coincide with C-bands. Euchorthippus pulvinatus is an exception; here NORs do not seem to be related to C-bands. However, the nucleolar-associated heterochromatin in this species can be demonstrated by a N-banding technique.Key words: nucleolar organizer, NOR (primary), C-bands, heterochromatin, NOR (secondary).