Rresearch workers should use correct genetic nomenclature in order to ensure that data in electronic databases is internationally consistent. An abbreviated version of the nomenclature rules is given here. The most recent version is given on the Jackson Laboratory web site.
Official rules for nomenclature of inbred strains
These were first formulated for mice in 1952 and have been revised several times since then. A Committee on Standardized Genetic Nomenclature for Rats was first established in 1979. It was reconstituted in 1994 following recommendations of a committee of the Institute of Laboratory Animal Research (ILAR). The rules are essentially the same as those used for the mouse. No official body governs nomenclature of other species but, with minor modifications, the rules devised for mice are suitable for all specie
Symbols to designate the strain
Strains are designated by brief symbols consisting of upper case letters and numbers, beginning with a letter, e.g. A, BALB, C3H, C57BL, NZB mice and ACI, F344, LEW and M520 rats. Exceptions are strains which were already widely distributed and used before the rules were formulated, such as strain 129P1. Note that it is incorrect to use a full descriptive name such as “Brown Norway” rather than the correct designation BN. In particular the full name is not amenable to the use of substrain symbols and laboratory codes which help to identify the animals which were used. Usually strain designations have no particular meaning. They are simply codes used when describing the strain.
Strains derived from a common ancestor but separated before F20 are related strains and the nomenclature should recognise this, e.g. NZB, NZC, NZO mouse strains and MHR, MNS rat strains. Such related strains should usually have at least the first letter in common so that they appear near each other in alphabetical lists. Where it is necessary to indicate the number of generations of inbreeding this can be shown in parentheses, e.g. (F150) or (F?+ 24) when previous inbreeding is unknown but there have been 24 generations of recent sib mating.
Substrains are regarded as having been formed when:
- Branches of an inbred strain were separated after F20 but before F40. This is because even that 1% of residual heterozygosity may be of scientific importance.
- A branch has been maintained separately from other branches for 20 or more generations . The existence of differences arising by mutation is then likely.
- Proven genetic differences from other branches are discovered. Such differences could have arisen either as a result of residual heterozygosity (i.e. there still some loci segregating at the time that the strain was divided) or of new mutations.
A non-strain mating is likely to lead to numerous genetic differences, and may thus be distinguishable from mutation. If contamination is though likely, the strain should be renamed. For example, mouse strain A2G was developed as a result of a contamination of strain A by an unknown mouse, followed by BxS mating.
Designation of substrains
Substrain symbols are appended to the strain name following a slanted line and may consist of either a number, e.g. FL/1, FL/2 (this is the preferred option with inbred strains of rats) or a laboratory registration code which designates the person or laboratory originating the strain or substrain, e.g. A/He, the Heston substrain of strain A. These codes have an initial capital letter, followed (where present) by lower case letters.
A combination of the above may also be used. Some exceptions are permitted for strains in which a different designation is already well known, such as C57BR/cd or BALB/c. Substrain symbols can be accumulated.
Laboratory Registration code
Differences in the phenotype of laboratory animals can arise as a result of both genetic and environmental influences. The composition of the diet, associated viruses, bacteria and parasites, and the physical environment can all change the characteristics of the animal. In some cases, viral infections such as the mouse mammary tumour virus may be passed from mother to offspring for many generations. For this reason, it is important to be able to distinguish between animals of the same strain and substrain, but originating from different sources.
Abbreviated strain names
In some circumstances it is helpful to be able to abbreviate the strain name so that compound names do not become too long. This is permitted, provided that the full strain name is given somewhere in the text, e.g. in the materials and methods section. The following abbreviated names of mouse strains are recommended:
F1 hybrids are the first generation of crosses between two inbred strains. They have many of the most useful properties of inbred strains. They are designated by listing the female strain first and the male strain second with “F1” appended. Abbreviated strain names are commonly used, e.g. B6C3F1 is the first generation cross between a C57BL/6 female and a C3H male. Note that the reciprocal F1 hybrids B6C3F1 and C3B6F1 mice differ in the Y chromosome and maternal influences, and should not be considered genetically or phenotypically identical.