One curiosity which arose during the genotyping of progeny from heterozygous interbreeding was the highly non-Mendelian ratio of Capn2+/+ (11.6%) to Capn2+/- (88.4%) of weanlings. At present, there is no obvious explanation for this result. Crosses between wild-type and heterozygous mice also produced progeny with a greater than expected proportion of heterozygous offspring. Interestingly, heterozygous crosses involving the Capn4 transgenic line generated by Zimmerman and colleagues yielded progeny with a similar, if less extreme, skewing in favor of the heterozygous genotype. Out of a total of 80 genotyped animals, 22.5% were wild-type and 77.5% were heterozygous, with no homozygous null progeny observed [32]. These observations suggest a developmental advantage associated with reduced calpain expression. Perhaps future studies will reveal a mechanistic basis for this.