Studies on radiation-induced chromosome aberrations in mouse spermatocytes II. Dose-response relationships of chromosome aberrations induced at zygotene stage in mouse primary spermatocytes following fast neutron- and 60Co γ-irradiations

Abstract

The chromosome aberrations induced at zygotene stage in mouse spermatocytes following exposures to fast neutrons and 60Co γ-rays were examined at diakinesis-metaphase I. The dose-response relationships were well fitted to linear equation for deletion-type aberrations and to linear-quadratic equation for exchange-type aberrations in 60Co γ-irradiation group. In fast neutron-irradiation group, the dose-response relationships were well fitted to linear equations for deletion- and exchange-type aberrations. The rate of deletion-type aberrations was remarkably high for fast neutrons, about 6 times higher than that after 60 γ-irradiation. The main types of chromosome aberrations observed were iso-chromatid breaks of fragments and chromatid exchanges in both irradiation groups as well as X-irradiation. These results indicate that there is a possibility that two double-strand breaks are induced simultaneously at iso-locus position in sister chromatids by a single track of radiations. Production of such single-track-induced two double-strand breaks in iso-chromatids may be very frequently expressed as iso-chromatid-type deletions in the high LET fast neutron-irradiation group. On the contrary, in the low LET 60Co γ- or X-irradiation group, the above-mentioned mechanism may not be so effective for contribution to chromosome aberration induction in mouse spermtocytes. This mechanisms was discussed in detail.