[Heterochromatic regions and chromosome 21 nondisjunction in man. II. A comparative analysis of the polymorphism of the C bands of chromosomes 1, 9 and 16 in the fathers and mothers of Down's disease children].

To test a hypothesis on potential role of large heterochromatic regions in chromosome non-disjunction, a comparative analysis of C segment lengths of chromosomes 1, 9, and 16 in fathers and mothers of children with Down's syndrome was carried out. No difference was found between the two groups. The non-disjunction in mothers is known to occur 4 times as frequently as in fathers. This fact does not allow to suppose that the heterochromatic regions may play a certain part in non-disjunction of chromosome 21.