The experimental induction of gynogenesis in the mouse I. Irradiation of the sperm by X-rays

Sperm of the mouse, M us musculus, was X-irradiated in vitro before fertilization. Dosages were between 100 and 50 000 r. With increasing irradiation of the sperm, the chromosome complement of embryos, scored at 3ijr days’ gestation, declined from diploid to haploid. Higher dosages increasingly retarded embryonic development, 30000 and 50 000r restricting development to the first cleavage. Gynogenetic development was very abortive. X-irradiation did not usually prevent male pronucleus formation or syngamy. Loss of paternal chromosomes occurred in the embryos during development, probably by the loss of chromosome fragments into sub-nuclei. After 30000 or 50 000r, abnormal pronuclear relationships were found. In some eggs, sperm entry and the growth of the male pronucleus did not stimulate completion of the second maturation division. In other eggs, the single pronucleus was probably female, the male pronucleus having degenerated. Polyspermy occurred at the same dosage. 1000r almost completely suppressed implantation. 500r caused considerable embryonic mortality. Irradiation damage to the centriole or cytoplasm of the sperm in addition to destruction of its chromosomes may have caused the retarded development of the embryos.