A study of the constitutive heterochromatin and nucleolus organizer regions of Isocopris inhiata and Diabroctis mimas (Coleoptera: Scarabaeidae, Scarabaeinae) using C-banding, AgNO3, staining and FISH techniques

Meiotic and mitotic chromosomes of Isocopris inhiata and Diabroctis mimas were studied by standard staining procedures, C-banding, silver nitrate staining and FISH using Apis mellifera 28S rDNA as probe. Isocopris inhiata presented a 2n = 18 (811+ Xy(p)) karyolype, composed of meta-submetacentric chromosomes with gradual reduction in size. The karyotype of D. mimas wets 2n = 20 (911+ Xy(p)), composed of meta-submetacentric (pairs 1, 2, 3, 4 and 7) and acrocentric (pairs 5, 6, 8 and 9) chromosomes, with gradual reduction in size. Analysis of constitutive heterochromatin revealed similar C-banding patterns for both species, showing pericentromeric and telomeric bands and diphasic chromosomes. In addition, the X chromosomes of these species were found to be almost completely heterochromatic. The presence of chromocenters was checked in one or more phases of prophase I of these species. All heterochromatin reacted positively for the silver stain. By FISH analysis we were able to locate the rDNA in medium-size autosome pairs in both species and in the X chromosome of D. mimas.