Dose-related chromosome non-disjunction in female mice after X-irradiation of dictyate oocytes.

The chromosome non-disjunction inducing effect of relatively large doses (100-600 cGy) of X-rays to various dictyate oocyte stages has been examined by chromosomal analysis of 1-cell embryos recovered from female mice 3.5-23.5 days after irradiation. Numerical chromosome anomalies, as a result of non-disjunction, occurred in significantly larger proportions of embryos from irradiated females compared to unirradiated controls. Moreover, non-disjunction was induced by X-irradiation in dose-related fashions which could be described by either quadratic or dose-squared curves. The different oocyte maturation stages sampled showed significantly different responses to X-irradiation. The most mature stage, sampled 3.5 days after treatment, was less responsive to the non-disjunction inducing effect of X-rays compared to other, younger maturation stages. Chromosome structural anomalies were also found significantly more frequently after X-irradiation of dictyate oocytes. Structural anomalies were induced in dose-related fashions in all oocyte maturation stages and could be described by either quadratic or dose-squared curves. A smaller proportion of embryos from females sampled at the shortest interval after irradiation contained structural anomalies compared to those from females sampled at the longer intervals. No evidence was obtained for a significant effect of X-irradiation on the frequency of triploid embryos.