A region of one or more chromosomes that contains the ribosomal RNA genes (q.v.) and is associated with the nucleolus (q.v.). Also called the nucleolus organizer region (NOR). See Chronology, 1934, McClintock; 1965, Ritossa and Spiegelman; 1967, Birnstiel; 1969, Miller and Beatty; 1976, Chooi; Cajal body, rDNA amplification, ribosome, RNA polymerase.
Nucleolus of maize chromosome 6. From L. W. Sharp, Fundamentals of Cytology, page 85. © 1943, McGraw Hill, NY.
Subjects: Genetics and Genomics.