APP - A Quick Review to the Nomenclature of Inbred Mice
Mice that can be traced to a single ancestral pair and have been mated,
brother to sister, for 20 generations or more are called inbred strains
of mice. All inbred mice are “strains”; all outbred mice
are “stocks”. Newly created inbred strains of mice are named
with uppercase letters and numbers, always beginning with a letter (CBA,
DBA, etc). Some inbred strain names currently in use are grandfathered
in from older naming conventions and do not follow current inbred naming
rules. For example, the BALB/c is correctly named with the “c” as
a lowercase letter and the 129 strains begin with numbers.
Substrains of mice are most commonly formed when 1) previously unknown
genetic differences are found within a strain or 2) if animals are separated
from their parent colony for more than 20 generations. In each case,
accumulation of mutations may result in genetic differences between the
substrains. These substrain differences may not have an impact
on your research, but only you can determine that fact. The
first substrain designation is separated from the main strain name by
a forward slash (“/”).
For example, C57BL/6 and C57BL/10 are both substrains of the C57BL strain.
Historical exceptions to this rule exist and one prominent one is the
BALB/c (the “c” is not a substrain designation). Further
separation within substrains may result in the formation of new substrains.
A laboratory code representing the movement of a strain from one holder
(laboratory, vendor, etc.) to another is added each time the strain is
transferred. An example of the addition of laboratory codes is below.
This mouse: #1. BALB/cN
Is different from this mouse: #2. BALB/cNCrl
Is different from this mouse: #3. BALB/cNCr
Is different from this mouse: # 4. BALB/cNCrlCr
In the above cases, the lettering for substrain #1 represents the original
BALB/c colony at NIH (N). Substrain #2 was moved to Charles River Laboratories
(Crl) and substrain #3 went to NCI, DCTD Animal Production Program which
is represented by the lab code Cr (Cancer Research) The final example
(substrain #4) is the establishment of the Charles River Laboratories
substrain (#2) back to NCI (designated Cr)
Given the fact that genetic differences will accumulate in substrains,
and that it is very difficult to determine if they will result in any
phenotypic differences, it is good practice to obtain animals of a particular
strain from a single supplier or run parallel experiments to be sure
different substrains react in the same way for your particular experiment.
For further information on the naming of inbred mice or mouse gene naming
conventions, please visit the following sites: