Most laboratory mice have contributions from both Mus musculus musculus and Mus musculus domesticus. There is evidence that smaller contributions also may have come from Mus musculus molossinus and Mus musculus castaneus. Therefore, they should not be referred to by species name, but rather as laboratory mice or by use of a specific strain or stock name. (In addition, some recently developed laboratory mouse strains are derived wholly from other Mus species or other subspecies, such as M. spretus). The laboratory mouse genome, including its retroelements, is a mosaic and an artificial creation, and there is no true "wildtype" laboratory mouse.
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There are over 450 inbred strains that have arisen during the last century but the great majority of biomedical resaerch, including genomic research, is based on a relatively few mouse strains, including C57BL/6, BALB/c, C3H/He, 129, FVB, and outbred Swiss stocks.