nucleolus organizing region ( nor ) activity in seven probands with down syndrome due to a de novo ( 21 ; 21 ) translocation and their parents was analyzed on the basis of total ag-nor size per cell , mean ag-nor size per cell ( xc ) , mean ag-nor size per acrocentic ( xa ) , and the characteristic ag-nor number of each subject .
C0007634
cell
C0007609
nor