The present invention is directed to the production, breeding and use of transgenic non-human animals such as mice in which specific genes or portions of genes have been replaced by homologues from another animal to make the physiology of the animals so modified more like that of the other animal with respect to drug pharmacokinetics and metabolism. The invention also extends to the use of the genetically modified non-human animals of the invention for pharmacological and/or toxicological studies.
