[en] The ploidy of the thymus was studied in C57B1/Ka mice irradiated with 4 weekly X-Ray doses of 1.75 Gy. The determination of nuclear DNA content was performed by flow cytometry of intact thymocytes labeled with propidium iodide in presence of a mixture of chicken and rainbow trout red blood cells as internal reference standards. The method has been tested by detecting the sex difference in DNA content of G0/G1 of normal thymic mouse cells. The mean value was 2.9% higher in female mice. The thymus of almost 60% of irradiated male mice present a slight hypoploidy of 2.6% one month after the last irradiation.
