This strain carries an inversion on Chromosome 1 that includes Pep3b and Idh1b. Homozygotes tend to get fat and breed poorly.
This inversion was identified in the offspring of a DBA/2J male treated with TEM. Little is known of how it was bred prior to cryopreservation, but it was bred to homozygosity. Embryos were generated for cryopreservation from C57BL/6J females bred to homozygous males. The inversion bears the Pep3b and Idh1b alleles, whereas the C57BL/6J Chromosome 1 has the Pep3a and Idh1a alleles.