that those 11 subspecies can be further grouped into four subspecies groups as follows: domesticus, bactrianus, castaneus, and musculus (Moriwaki 1994; Moriwaki and others 1990). Genetic divergence time among them has been estimated to be approximately one million years (Moriwaki and others 1979; Yonekawa and others 1981). In these studies, the genetic origin of the laboratory mice was identified as mostly European wild mice (Yonekawa and others 1982). The implication of this finding is correct, that more genetic variations should be found between the Asian wild mice and laboratory strains. The percentage of variation in the microsatellite DNA polymorphism between the Asian mice and laboratory mice was significantly greater than within laboratory mouse strains (95% vs. 48%) (Shiroishi and others, unpublished data).

In 1982, Shiroishi and colleagues discovered a remarkable recombination hot-spot in a Japanese wild-derived major histocompatibility complex (MHC) chromosome. The frequency of meiotic recombination in the MHC chromosome with this hot-spot is more than 100 times greater than normal (Shiroishi and others 1982). Hattori and others (1999) introduced this hot-spot chromosome segment into the NOD diabetes model mouse and obtained various recombinants in the MHC region. Their comparison between the incidence of diabetes and the introduced chromosome segments indicates the possible presence of three genes at 5' upstream of the H2- K-I region, already reported to be important in the control of diabetes.

In 1995, Kaneda and colleagues developed mitochondria congenic strains that carry mitochondria of either the Asian wild-derived Mus musculus musculus subspecies or the European wild-derived Mus spretus species (Kaneda and others 1995). Both are genetically quite remote from laboratory mouse strains. In 1998, Nagao and colleagues demonstrated decreased physical performance of the congenic strains with a mismatch between the nuclear and mitochondrial genome, that is, the genetic background (Nagao and others 1998).

In 1999, Shiroishi and others (unpublished) attempted to develop new inter-subspecific consomic strains. Each of the 19 autosomes, X and Y chromosomes