Radiation-induced translocations in spermatogonia of mice

The translocations considered in the present review are only the reciprocal translocations that involve exchange of terminal segments between non-homologous chromosomes and therefore require two breaks and rejoins. During many years this type of translocation has been ascertained by analyzing the F1 progeny of treated and control animals for heritable semi-sterility, but at present the translocations induced in spermatogonia are studied by cytological techniques in the derived spermatocytes because at diakinesis-first metaphase stage of meiosis the homologous chromosome segments of the rearranged and interchanged chromosomes will pair to form characteristic translocation configurations. The kinetics of the translocation inductions show that some observations fit very well with a two-event process but that others seem to be in better agreement with the postulate that translocation induction is mainly the result of a one-track process. No statistical difference between the strains of mice is observed with respect to the rate of affected cells. Some decrease in the yield of spermatocytes with translocation configurations is found for long intervals of time between irradiation and observation. The analysis of the F1 progeny derived from irradiated spermatogonia shows that the frequency of translocated offspring is always much lower than expected from the rate of translocated spermatocytes in the irradiated animals.