The Rat Gene Map.

The Norway rat (Rattus norvegicus) was the first mammal to be domesticated primarily for research purposes, perhaps as many as 150 yr ago. The rat is 1 of the 2 most widely used experimental animals in biomedical research; and a wealth of knowledge, primarily in physiology, is available (Jacob and others 1995; James and Lindpaintner 1997). Many genetically defined strains have been developed and maintained. Some strains display specific susceptibility to complex traits such as hypertension, diabetes, arthritis, or cancer; and others evidence certain immune dysfunctions or neurobiological disorders (Hedrich 1990). When attempting to elucidate the role of genetic and environmental factors that underlie such diseases, studies with these models will be extremely useful complements to research on human subjects (Gill and others 1989).