A study of meiotic pairing, nondisjunction and germ cell death in laboratory mice carrying Robertsonian translocations.

Frequencies of anaphase I nondisjunction, germ cell death and pairing abnormalities at pachytene were assessed in male mice singly heterozygous and homozygous for the Robertsonian (Rb) translocations: Rb (1.3)1Bnr, Rb(11.13)4Bnr and Rb(10.11)8Bnr. Rb homozygotes showed low frequencies of nondisjunction but substantial germ cell death. This germ cell death could not be attributed to problems at pachytene as Rb homozygotes showed no increase in pairing abnormalities over the (C3H/HeH x 101/H)F1 controls. Instead genic factors are involved. Rb heterozygotes showed substantial frequencies of nondisjunction and even greater germ cell death than found in the homozygotes. Pachytene pairing abnormalities were observed and it appears that these, together with genic factors, cause physiological perturbation of meiocytes, thereby promoting germ cell death, with nondisjunction of the trivalent as a sublethal response.