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 heterozyg ous and homozygous for the Robertsonian (Rb) translocations: Rb (1.3)1 Bnr, Rb(11.13)4Bnr and Rb(10.11)8Bnr. Rb homozygotes showed low freque ncies of nondisjunction but substantial germ cell death. This germ cel l death could not be attributed to problems at pachytene as Rb homozyg otes showed no increase in pairing abnormalities over the (C3H/HeH x 1 01/H)F1 controls. Instead genic factors are involved. Rb heterozygotes showed substantial frequencies of nondisjunction and even greater ger m cell death than found in the homozygotes. Pachytene pairing abnormal ities were observed and it appears that these, together with genic fac tors, cause physiological perturbation of meiocytes, thereby promoting germ cell death, with nondisjunction of the trivalent as a sublethal response.