title: Genetic determination of NOR activity in human lymphocytes from twins.
abstract: Activity of nucleolar organizer regions (NORs) was studied in cultured blood lymphocytes from 20 monozygotic (MZ) and 20 dizygotic (DZ) twin pairs. The number of Ag-stained NORs, the degree of staining, and the frequency of acrocentric associations were used as criteria of the NOR activity, the acrocentric chromosomes being identified by G-banding. Analysis of intrapair concordance as well as of intrapair variance showed the number of Ag + NORs and the size of Ag-deposits to be highly heritable traits. Intrapair differences in acorocentric association frequency were not significantly higher in DZ compared with MZ twins.
mesh_terms: D000328:Adult; D001399:Azure Stains; D002871:Chromosome Banding; D005260:Female; D005796:Genes; D006801:Humans; D008214:Lymphocytes / Q000648:ultrastructure*; D008297:Male; D008875:Middle Aged; D009697:Nucleolus Organizer Region; D011247:Pregnancy; D012835:Silver Nitrate; D014427:Twins
chemical_list: D001399:Azure Stains; D012835:Silver Nitrate