Multi-chromosomal location of ribosomal RNA genes and heterochromatin association in brown trout

Abstract
The ribosomal rRNA genes have been mapped by fluorescentin situ hybridization (FISH) to brown trout chromosomes. One major NOR chromosome pair and 8 novel minor NOR chromosome pairs have been found. Both major and minor NORs were closely related to polymorphic heterochromatin, as revealed by FISH and C-banding. These results are discussed with respect to NOR expression, the relationship between rDNA and heterochromatin, and evolutionary aspects.