X-ray induction of chromosome and chromatid aberrations in the same cells after treatment with hydroxyurea

Vicia faba root meristem cells treated for 24 h with 1.25 mM hydroxyurea and then X-irradiated contained a large number of cells with both chromosome and chromatid aberrations. X-irradiation 4 h after release from the hydroxyurea block yielded cells with almost exclusively chromatid aberrations.