with chimpanzees (98.7% with bonobos) and over 90% with the mouse. With so much of the genome conserved across species, it is relatively impressive that the differences between humans and mice can be accounted for in approximately six thousand genes (of ~30,000 total). Scientists have been able to take advantage of these similarities in generating experimental and predictive models of human disease. Disease models Animal models serving in research may have an existing, inbred or induced disease or injury that is similar to a human condition. These test conditions are often termed as animal models of disease. The use of animal models allows researchers to investigate disease states in ways which would be inaccessible in a human patient, performing procedures on the non-human animal that imply a level of harm that would not be considered ethical to inflict on a human. As in noted the introduction, animal models can be classified as homologous, isomorphic or predictive. Animal models can also be more broadly classified into four categories: 1) experimental, 2) spontaneous, 3) negative, 4) orphan. Experimental models are most common. These refer to models of disease that resemble human conditions in phenotype or response to treatment but are induced artificially in the laboratory. Some examples include: The use of metrazol (pentylenetetrazol) as an animal model of epilepsy Immunisation with an auto-antigen to induce an immune response to model autoimmune diseases such as Experimental autoimmune encephalomyelitis Occlusion of the middle cerebral artery as an animal model of ischemic stroke Injection of blood in the basal ganglia of mice as a model for hemorrhagic stroke Sepsis and septic shock induction by impairing the integrity of barrier tissues, administering live pathogens or toxins Infecting animals with pathogens to reproduce human infectious diseases Injecting animals with agonists or antagonists of various neurotransmitters to reproduce human mental disorders Using ionizing radiation to cause tumors Using gene transfer to cause tumors Implanting animals with tumors to test and develop treatments using ionizing radiation Genetically selected (such as in diabetic mice also known as NOD mice) Various animal models for screening of drugs for the treatment of glaucoma The use of the ovariectomized rat in osteoporosis research Use of Plasmodium yoelii as a model of human malaria Spontaneous models refer to diseases that are analogous to human conditions that occur naturally in the animal being studied. These models are rare, but informative. Negative models essentially refer to