[WR, a new strain of mice, highly sensitive to the cytogenetic effect of thiotepa].

Mice of the WR strain (genotype -aa, +WY) were selected for the appearance of black spots with normal pigmentation, presumably due to genetic recombination in the W gene region. The frequency of heterozigotes +WY with black spots was 25% in the 11th generation. The cytogenetic effect of thioTEPA (dose 5 mg/kg) was investigated in bone marrow cells of C57BL/10 NZW, 101/H and 129/Re mice. Mice of the WR strain were most sensitive to thioTEPA. It is suggested that the WR mice may be used as a sensitive object for the genetical screening of chemical compounds.