[Heterochromatic regions and the nondisjunction of human chromosome 21. I. Polymorphism of the C-bands of chromosomes 1, 9 and 16 in children with Down's syndrome].

To test a hypothesis on potential role of large heterochromatic regions in chromosome nondisjunction polymorphism of C segments of chromosomes 1, 9, and 16 in 70 children with Down's syndrome were examined. The C segment lengths of the above chromosomes were shown not to deviate from the normal. To solve the problem, it seems unreasonable to examine children with Down's syndrome.