**4.6 N (Nucleolar organizing regions) banding**

The NOR regions could be selectively stained by techniques involving either giemsa or silver staining. The giemsa technique developed by Matsui and Sasaki [29] allows the staining NOR after extraction of nucleic acids and histones. The technique N banding was improved by Funaki et al. [30]. The silver staining technique fall into two categories; a) Ag-As method: the method is based on the staining with combined silver nitrate and ammoniacal silver solutions; b) Ag method: in this method, staining with ammoniacal silver is omitted. NOR banding stains only those regions that were active as nucleolus organizers in the preceding interphase as well as useful for visualization and study of satellite associations.
