[Expression of the mutant gene mi in mice: white spotting pattern].

Mice of mi/+ and +/+ genotypes of the mutant stock microphthalmia (mi) were mated inter se and with those of CC57BR/Mv and CBA/J inbred lines. In all types of crosses, the offsprings of mi/+ genotype had unpigmented fingers and distal tail parts (penetrance 100%). This trait is determined mostly by the mutant mi gene, the expression of which is not affected by modifier genes. However, the degree of mi gene expression, white spotting, on other body parts (wrist, foot, ventral body side, and parietal head part) varied widely in mice obtained from different crosses; penetrance ranged from 0 to 100%. The results obtained indicate that in these cases, the expression of mi gene was strongly affected by modifier genes. The different frequency of the mi gene effects, in heterozygote offspring obtained from reciprocal crosses, can result from the imprinting of the modifier genes in maternal and paternal gametes.