Studies on the karyotype differentiation of the norway rat. IX. Translocation between pair Nos. 4 and 7 occurred in a WM strain rat after .GAMMA.-irradiation, with special regard to the segregation in F1 hybrids involving an XYY male.

A male WM strain rat with 4/7 translocation was obtained in the offspring born after γ-irradiation. The male with translocation was mated to the normal females, and 14 offspring was obtained. They were segregated to the translocation heterozygotes (7) and the non-translocation rats (7) as just expected. Among the latter rats, one had the XYY sex chromosomes which were suggested to be developed by non-disjunction of the Y element in the meiosis of the translocation male parent.