There are hundreds of pathological mutants in mice and rats, and
many of these are of interest to biomedical research. Such mutants
have a Mendelian mode of inheritance. While an inbred strain may be
used by investigators in many fields, a mutant is generally used
for very specialized projects.
For example, the obese mouse is invaluable for studies
associated with metabolism and physiology, but is seldom used in
other fields or investigations. However, athymic nude mice have
already made a substantial contribution to many scientific
disciplines, such as immunology and cancer research.
Mutant mice can be maintained with either outbred or inbred
genetic backgrounds. The properties of the outbred or inbred
background therefore determine the genetic advantages and
disadvantages. For example, the athymic nude gene on the outbred
HsdCpb:NMRI background produces a relatively robust animal, but
animals with BALB/cOlaHsd background are less robust.