Source:http://linkedlifedata.com/resource/umls/id/C0600529
MSH: Inbred strains of animals that are genetically identical except at a single locus, or a few specified loci, so that their known genetic differences are expressed in the same genetic background. A congenic strain is produced by outbreeding a strain and then eliminating the background by many generations of backcrosses while maintaining the desired genetic differences by selection of progeny. (Dorland, 28th ed)