C57BL/6 is classified as an inbred, which results from a crossing of no less than 20 consecutive generations of brother-sister matings. This allows the offspring to possess both genetic and phenotypic uniformity. As with most inbred strains, reproductive performance is lowered, along with the general size of the mouse and its overall lifespan, in comparison to its outbred counter part. Some of the typical characteristics that one finds in a C57BL/6 include:

• High alcohol and morphine preference.
• Low incidence of mammary tumors.
• Resistance to audiogenic seizures.
• High susceptibility to diet-induced atherosclerosis.
• High incidence of microphthalmia.
• Susceptibility to chronic ulcerative dermatitis.
• Resistance to radiation.
• Resistance to anaphylactic shock.
• Age related hearing loss is common at 12-18 months of age.
• Average litter size of 6-8pups and weaning occurs at 20 days of age.

The female C57BL/6 are used commonly for embryo donation. They superovulate well, and they are popular for DNA microinjection. The blastocysts from C57BL/6 are commonly used as recipients for embryonic stem cells when creating "knockouts". The females can be poor mothers, however. It is not uncommon to statistically see high newborn mortality rates and cannibalization from first time mothers.