Condensed Strain Nomenclature Guidelines


The complete guidelines for strain nomenclature can be found at /nomen/rules-for-nomen.shtml.



Strain Type



Inbred Strain

Mated brother x sister or youngest parent x offspring for 20+ consecutive generations.

Symbol designated by capital letter or letters (four letters or fewer) in Roman type; e.g. BN, SHR

Related Inbred Strain

Strain with common origin but separated before F20.

Symbol should indicate the relationship. Symbols should be together in the alphabetical list; e.g. SS, SR


Genetically diverged inbred strains due to:

1.separation after 20 but before 40 generations of inbreeding 2.observation of genetic differences (residual heterozygosity or mutation) between branches 3. separation of branches for 20+ generations.

Name of the parent strain, slash, ILAR code (Institute for Laboratory Animal Research Up to three ILAR codes can be added in a symbol; e.g. WKY/N, BN/NHsdMcwi

Recombinant Inbred Strain

Formed by crossing 2 inbred strains followed by 20+ generations of brother x sister mating.

Abbreviation of both parental strain names separated with capital X with no space. Different RI strains in a series are distinguished by numbers following the symbol; e.g. BXH1, BXH2

Coisogenic Strain

Inbred strains that differ at only a single locus through mutation occurring in that strain.

Strain symbol or substrain symbol followed by a hyphen and the gene symbol of the differential allele in italics followed by the ILAR code of the lab; e.g. BN-RT1n/Rj

Congenic Strain

Produced by repeated backcrosses to inbred (background) strain with selection for a particular marker from the donor strain. Minimum 10-backcross generation to the background strain should be made.

Abbreviated symbol of the recipient strain, period, abbreviated symbol of the donor strain, hyphen, the differential allele (in italics), slash, ILAR code of the lab. If a chromosomal segment has been transferred list the most proximal and the most distal markers in parenthesis separated by a hyphen (in italics); e.g. LEW.BN-tl, SHR.BN-(D13Arb5-Ren)/Ipcv

Consomic Strain/Chromosome Substitution Strain

Produced by repeated backcrossing of a whole chromosome onto an inbred strain. Minimum of 10 backcross generations is required.

Abbreviated host strain, hyphen, chromosome number, strain of origin in superscript, followed by a slash, ILAR code of the lab; e.g. SS-2BN/Mcwi

Segregating Inbred Strains

Inbred strains in which a particular allele or mutation is maintained in heterozygous state.

Named as inbred strains with the segregated locus is a part of the standard genotype

Conplastic Strain

Nuclear genome from one strain has been crossed onto the cytoplasm of another, mitochondrial donor is always the female parent.

Abbreviated strain with the nuclear genome, hyphen, mt (mitochondrial) in superscript, strain of the cytoplasmic genome

Transgenic Strain

Any DNA that is stably introduced into the germline of a rat.

Symbol of the strain followed by hyphen then Tg denoting transgenic strain, in parentheses, the official gene symbol of the inserted DNA followed by then laboratory’s line or founder designation or a serial number slash the ILAR code of the originating lab; e.g., SD-Tg(GFP)Bal/2Rrrc.

Targeted mutations

Mutations/deletions/disruptions of gene targeted by homologous recombination

Symbol of the strain followed by hyphen then symbol of the targeted gene then superscript consisting of three parts tm to denote targeted mutation, serial number of the lab of origin and the ILAR code of the lab; e.g., (Mouse strain) 129-Trp53tm1Holl