Origin of the extra chromosome in trisomy 16.

Chromosome analysis was carried out on 22 spontaneous abortuses with trisomy 16 and their parents by means of sequential Q- and C-banding techniques. In seven cases, the extra chromosome No. 16 originated from a non-disjunctional error in the first meiotic division in the mother, and in two cases from an error in the first meiotic division in the father. In two cases, non-disjunction had occurred during the second meiotic division (one in the mother and one in the father). It seems that trisomy 16, although independent of maternal age, most frequently results from a first meiotic non-disjunction in the mother.