A species of organism commonly used for scientific study. Such species are generally chosen because they are relatively easy to work with and maintain in the laboratory and because often they are bred under strictly controlled conditions, with well-documented pedigrees, enabling comparison of results in different centres around the world. They range from the humble thale cress (Arabidopsis thaliana) to the long-suffering laboratory mouse (Mus musculus). A list of the most common model organisms is given in Appendix 5.