In practice, although not in theory, the subject of this chapter – the genetic determination of body scents that distinguish one individual from another individual of the same mammalian species – is fairly new. Systematic work on this topic was made possible by certain incidental observations made by animal technicians responsible for deriving and maintaining congenic mouse strains in a special facility for that purpose at Sloan Kettering Institute, in New York, USA.

Studies on the major histocompatibility complex (MHC)

In general, mice of an inbred strain are genetically identical to one another. Mice of an inbred congenic strain are likewise identical with one another and differ from a selected standard inbred strain only in the vicinity of a particular gene or gene complex. This discrete genetic difference between a pair of congenic strains, meaning a standard inbred strain and its congenic companion strain, is achieved by crossing two inbred strains and then serially back-crossing to the selected inbred parental strain for many generations with selection for an allelic genetic trait of interest, derived from the opposite parental strain, in each generation. Any difference that distinguishes a pair of congenic strains, provided that this is shown to be genetic by appropriate segregation tests, must be due to the selected gene or a gene in that vicinity, i.e. within the small segment of donor chromosome carried over together with the selected gene (Boyse, 1977; Foster et ai, 1981).