Similar dose-related chromosome non-disjunction in young and old female mice after X-irradiation.

Radiation-induced chromosome non-disjunction has been investigated in young and old female mice. Chromosome numbers were screened in maternal and paternal pronuclei of 1-cell embryos. To avoid bias due to preparatory artefacts, only the numbers of hyperploid pronuclei were used as measures of chromosome non-disjunction. Spontaneous non-disjunction occurred more frequently in oocytes of old females (1.54%) compared to young females (0.19%). After X-irradiation, both young and old females displayed significant linear increases in non-disjunction with absorbed dose. The slopes of the regressions did not differ significantly. Maternal pronuclei of 1-cell embryos recovered from irradiated females occasionally contained chromosome structural aberrations. The numbers of aberrations showed significant linear relationships to absorbed dose in young and old females. No significant difference was present between the numbers of aberrations in young and old females. Analyses of numerical and structural chromosome anomalies have demonstrated, therefore, no increase in sensitivity to radiation to occur with maternal age.