X-ray-induced chromosome aberrations in mouse dictyate oocytes. I. Time and dose relationships.

Structural chromosome aberrations were analyzed in superovulated metaphase-I oocytes of the mouse, Mus musculus, at various times after a single acute dose of 200 R of X-rays. The aberrations seen were of the chromatid type, i.e., chromatid interchanges, isochromatid deletions and chromatid deletions. The aberration frequency was low during the interval 24 h to 5 days between irradiation and ovulation; peak frequency was reached when irradiation was given 14 days prior to ovulation. A dose-response study was made 14 days prior to ovulation at doses of 50, 100, 200, 300 and 400 R. A curve of these data indicated that a significant two-track component was present for both interchanges and deletions. Centromere staining revealed that symmetrical and asymmetrical interchanges occurred at approximately equal frequency and also that the asymmetrical equivalent of crossing-over was induced at a measurable frequency.