Maintaining a breeding colony of wildtype mice:
A practical overview of population genetics
To maintain genetic diversity (heterozygosity) over multiple generations, a large population of
breeding animals must be used. Small breeding populations experience genetic bottlenecks, which
reduce variability in the population and create genetic drift away from the original population.
Why is preventing genetic drift in wildtype animals important? To duplicate a study requires using
the same strain of animals as previously used, sometimes even from the same vendor. If you are
using wildtype animals that you have maintained for several generations, your animals carry genetic
alleles at different frequencies than those from the commercial vendor. Some alleles in your
population may have even disappeared.
As an example of the colony size needed to maintain diversity, one commercial vendor keeps at least
200 cages of breeding pairs for a single wildtype strain. Even with a colony of 200 breeding cages,
some genetic drift will creep in. One vendor with multiple breeding locations annually replaces 20%
of the breeding stock at a given location with animals maintained at another of their locations.
At 2010 per diem rates, maintaining 200 breeding mouse cages costs nearly a thousand dollars a
week. Those breeding pairs will produce one to two thousand pups every 3 weeks requiring
considerable amounts of time to manage the colony, conduct weaning, etc. Economies of scale are
only approached when thousands of wildtype mice are needed at each generation. In the end, it is
generally more time and cost efficient to purchase heterozygous animals from commercial vendors as
needed.
The sample breeding scheme outlined below maintains a paternal lineage, by continually using males
from one line and adding a female from a different line.
Larson 2010