A strain is defined as inbred when it has been mated brother x sister for 20 or more consecutive generations (F20). All offspring can be traced back to a single ancestral breeding pair in the 20th or subsequent generation. Such inbred strains are therefore isogenic (genetically identical). Each inbred strain has a unique genotype and consequently a unique phenotype. Phenotypical differences between inbred strains should be taken into account when designing experiments. Specific strains have been developed for a high incidence of tumors, unique pattern of behavior, specific immune responses, susceptibility to spontaneous diseases and other characteristics.

ORIGIN: Okamoto, Kyoto School of Medicine, 1963, from outbred Wistar Kyoto male with marked elevation of blood pressure mated to female with slightly elevated blood pressure. Brother x sister mating with continued selection for spontaneous hypertension was then started. To NIH in 1966 from Okamoto at F13. To Charles River from NIH in 1973 at F32.To BioLASCO Taiwan in 2006 from Charles River Laboratories.
COAT COLOR: White (albino)
RESEARCH APPLICATION: genetic hypertension, hypertensive drug research, ADHD model, safety and efficacy testing

 Wistar Kyoto (WKY) Rat, Nomenclature : WKY/NCrl

ORIGIN: Outbred Wistar stock from Kyoto School of Medicine to NIH 1971. This is the same stock from which the SHR/N strain was developed. To Charles River in 1974 from NIH at F11. To BioLASCO Taiwan in 2006 from Charles River Laboratories.
COAT COLOR: White (albino)
RESEARCH APPLICATION: control for the SHR rat, ADHD model

Lewis Rat, Nomenclature : LEW/Crl

ORIGIN: Developed by Dr. Lewis from Wistar stock in the early 1950s. To Charles River from Tulane in 1970 at F34.To BioLASCO Taiwan in 2011 from Charles River Laboratories.
COAT COLOR: White (albino)
RESEARCH APPLICATION: Transplantation research, induced arthritis/inflammation, experimental allergic encephalitis, STZ-induced diabetes