CYTOGENETIC PECULIARITIES IN THE ALGERIAN HEDGEHOG - SILVER STAINS NOT ONLY NORS BUT ALSO HETEROCHROMATIC BLOCKS

Hedgehogs belong to one of the several mammalian taxa in which karyoty pe differences are based on variations in heterochromatin content. Fur thermore, the number and location of nucleolar organizer regions (NORs ) can also vary widely In the present study these cytogenetic features were investigated in the Algerian hedgehog, Erinaceus (Aethechinus) a lgirus. The heterochromatin and NOR distribution patterns in the karyo type of this species are new among hedgehogs, whereas the euchromatic regions, including their G-band pattern, are similar to those reported by others. In addition, silver staining revealed a cytogenetic featur e exclusive to the heterochromatic blocks of E. algirus: their silver staining with standard cytogenetic procedures. Because no similar phen omenon has been described previously in a mammalian species, several h ypotheses about the significance and specificity of silver staining to NOR sites are discussed. Finally, the existence of different types of heterochromatin in the species analysed here, lead us to propose that what hedgehogs have inherited from their common ancestor is a mechani sm which permits the accumulation of heterochromatin on specific chrom osomes, rather than the heterochromatin itself.