The dose-effect curves for half and full translocations induced in mature sperm with the break points within the same chromosomal region were obtained. Probability of reunion q and the number of breaks N that could be calculated from these curves varies within the range 0.83-0.69 and 0.011-0.078, respectively. The half and full translocations were induced under maternal effect of mus 104D1. In this case, q = 0.86 (for normal genotype 0.79) and N = 0.114 (for normal genotype 0.048). These figures show that the dose increase and the introduction of the mus 104 cause increase in the breaks number and only weak change in break reunion occurs. The method developed can be used for the search for mutations that interfere with break reunion.