Chromosomal localization and activity of nucleolar organizer regions in the dog (Canis familiaris)

Using fluorescent in situ hybridization on Q-banded chromosomes, nucleolar organizer regions (NORs) were localized on canine chromosomes 7qter, 17qter, Yqter and also terminally on a small autosome, not yet included in the dog standard karyotype. The analysis of NOR activity was carried out on Ag-I stained metaphases originating from 27 individuals (10 males and 17 females). The mean number of silver stained NORs was 6.0 in males and 5.3 in females and the modal number was 7 and 6, respectively. Interindividual variability of the mean and modal numbers of silver NORs was observed. The lowest individual mean number of NORs was 4.2 and the highest 7.0, and the modal value ranged from 4 to 7. (C) Inra/Elsevier, Paris.