[Study on structural variation of nucleolar organizer regions (NOR) and the satellite association (SA)]

To further illustrate the biological significance of variant NOR (including double NOR--dNOR and triple NOR--tNOR) and satellite association (SA) and the relationship to meiotic non-disjunction (NDJ), this study was carried out in the normal population and the parents of patients with Down Syndrome (DS). Of 800 individuals, 4 dNOR carriers, two of them from the control and two from the non-informative experiments were detected. SA data for 3 out of the 4 dNOR carriers showed no statistical significant increase in SA when dNOR was present in the cell even in case 4 where two dNOR were found in one cell. However, ease 3 demonstrated significant decrease in SA when dNOR was present, although it showed that the overall incidence of dNOR was higher in this carrier than that in the other three. It is concluded that dNOR can be detected on any acrocentric chromosome and not be related to NDJ of chromosome, which is a heritable variant that does not affect phenotype and that there are two kinds of dNOR variants, one being from the translocation of the short arm of acrocentric chromosome, the other from non-translocation.