[Polymorphism of C-heterochromatin chromosome regions in the etiology of human aneuploidy].

Cytogenetic study of the C-heterochromatic polymorphisms in 202 individuals from the Down's syndrome families and in 31 control individuals was undertaken. In 58 families the source of an additional chromosome was taken into account. It was shown that in the donors of extra chromosome, due to nondisjunction in the Ist meiotic division, the frequency of heteromorphism was higher (0.61) than in other groups: donors with the 2nd meiotic nondisjunction (0.44), partners of donors (0.48) and controls (0.46). Also, increase in heteromorphism rate was found in a group of young mothers (0.56) compared with a group of old mothers (0.45). The role of heterochromatic regions in chromosome nondisjunction is discussed from the point of view of meiotic nonhomologues coordination.