ABSTRACT
Finding a mouse with an abnormal phenotype is not a rare observation in an animal facility. In some instances, this can be the consequence of infectious diseases, abnormal environmental parameters, intoxication, or any other acquired condition. When this is the case, one may find other individuals with the same phenotype, but, unless the causative agent is properly identified, such phenotypic deviants will be of little use as animal models. In other instances, the abnormal phenotype has a genetic origin, be it the consequence of a mutation in a single gene or due to the effect of a particular allelic combination.
