title: NOR variability in twins.
abstract: The number of AgNOR (NOR+) and the amount of AgNOR (NORM+) were analysed by means of two multilevel analyses of variance in a total of 12 twin pairs: 3 female and 4 male MZ and 5 male DZ pairs. In the first analysis, only zygosity was controlled; in the second, chromosome types D and G were controlled as well as the interaction between chromosome type and zygosity. For NOR+ and NORM+, when chromosome types D and G are not distinguished, the within-pair variance is greater, though not significantly, in DZ than in MZ pairs; but it is highly significantly greater when chromosome type (D or G type) is under control. This confirms an important genetic determination of NOR+ and NORM+ when in the ANOVA model the D and G types are controlled. However, nongenetic factors also influence the Ag-NOR patterns, but not enough to conceal the genetically defined rDNA pattern. Indeed, about 50% of the cells transcribe their rDNA in a way not closely dependent on the rDNA background and significant intrapair differences of NOR+ pattern exist in MZ twins.
mesh_terms: D000704:Analysis of Variance; D002871:Chromosome Banding; D003582:Cytogenetics; D005260:Female; D014644:Genetic Variation; D006801:Humans; D008297:Male; D012335:RNA, Ribosomal / Q000096:biosynthesis* / Q000235:genetics; D014427:Twins; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic
chemical_list: D012335:RNA, Ribosomal