HETEROCHROMATIC C-BAND POLYMORPHISM IN ET IOLOGY OF HUMAN ANEUPLOIDY

Cytogenetic study of the C-heterochromatic polymorphisms in 202 indivi duals 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 chrom osome, due to nondisjunction in the Ist meiotic division, the frequenc y of heteromorphism was higher (0,61) than in other groups: donors wit h 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 coordina tion.