[Chromosomal investigations in two age groups of human females].

Chromosomal analysis was performed in cultured lymphocytes from 32 old (ages 76-85, abbr. A) and 31 young (ages 15-20, abbr. J) patients, who were representative for a great part of the "normal" female population of the same age. In regard to culture time (48 and 72 hours) each age group was divided into two halves; 1500 cells were examined in each of the resulting four sub-units (A 48, A 72; J 48, J 72). Whereas the frequency of "spontaneous" gaps showed no dependency from age or culture time, single chromatid breaks were predominantly observed in A 72 and dicentric chromosomes in A 48. The mean breakage rates in the two age groups (A 48 2,4% A 72 3,0%; J 48 1,3%, J 72 1,7%) differed significantly for both culture times (Chi2 -test: A 48/J 48 p less than 0,01; A 72/J 72 p approximately 0,01). After karyotyping and additional application of a trypsin-Giemsa-branding-technique large, acentric "fragments," which could only be detected in metaphases of old females (A 48 1,0%, A 72 0,5%), proved to be X-chromosomes with premature centromere division and a high tendency to non-disjunction. These results are in agreement with those published by Fitzgerald (8).