Trisomy and triploidy induced by X-irradiation of mouse spermatocytes.

Analysis of second meiotic metaphase divisions in control and irradiated male mice shows that while the spontaneous rates of autosomal and sex chromosomal anaphase I non-disjunction are extremely low, they can be enhanced by X ray treatment of prophase spermatocytes. Irradiation at pre-leptotene results in a higher rate of anaphase I non-disjunction than does irradiation at pachytene. Early spermatogonia are relatively insensitive. Experiments to detect trisomic progeny among the F1 foetal offspring of male mice mated during weeks 5 and 6 following irradiation (sampling of irradiated early spermatocytes and late spermatogonia) showed that none were present. Possible explanations for this are considered. Two triploid foetuses were however found.