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[Double satellites do not increase the risk of chromosome 21 nondisjunction].

The hypothesis concerning the increase of the risk of appearance of offsprings with trisomy 21 in parents having double satellite acrocentric chromosomes is checked. Chromosomes of 266 parents having offsprings with Down's disease were examined, including 73 donors of extrachromosome 21. The frequency of chromosomes with dNORs in the total and in the donor groups did not differ from that of the control group. From 42 donors of extrachromosome, who demonstrated a nondisjunction in the first meiotic division, double satellites were revealed only once. In addition, data on the frequency of Dp+ and Gp+ variants are presented and discussed.