抄録
A familial survey was made to assess the origin of the extra chromosomes in a case of 13-trisomy and in 36 cases of Down's syndrome (30 regular 21-trisomies, 3 mosaics, and 3 translocations), using the fluorescent markers. The extra element in the 13-trisomy was due to the non-disjunctional error in the 1st meiotic division of the mother. In a sporadic 21/21 translocation Down's syndrome, the translocation appeared to have taken place in the paternal germ cells. Six informative cases were obtained for the rest of the cases. The maternal non-disjunction was responsible for 5 cases (1st division in 1 case, 2nd in 2 cases, and 1st or 2nd in 2 cases), whereas in the remaining 1 case the error occurred in the paternal 2nd division.
