Generation Definitions

Mouse strain generation numbers provide additional information on the genetic background and breeding history of mouse strains that cannot be captured in the mouse strain names. The symbols and definitions for mouse generation numbers used by The Jackson Laboratory are listed below.


Number of backcross generations.
Examples: N1, first backcross generation; N2, second backcross generation.


Filial or inbreeding (sister X brother) generations.
Examples: F1, first filial generation; F2, second filial generation.


Designates the generation when a strain was cryopreserved.
Example: F10p indicates a strain that was inbred for 10 generations and then cryopreserved.


Indicates the generation of a strain upon arrival at The Jackson Laboratory. Generation numbers before the "+" took place in the lab of the donating investigator; after the "+", at The Jackson Laboratory.


Used when the prior breeding history of a strain is not known.
Example: F?+F12, after arrival at The Jackson Laboratory, we interbred for 12 generations, prior to that remains unknown.


N-Equivalent is used when a mouse from a subsequent backcross generation is crossed back to a mouse from a prior backcross generation.


Generation is used primarily in mutagenesis schemes.
Examples: G0 is the mutagenized generation; G1 is the first generation after mutagenesis.