**1.3.2 Genetic stability control**

The continuous passing of live animals in a small population may lead animal strains to accumulate spontaneous mutations and undergo genetic drift. In mouse, as an example of a lower mutation rate because of its relatively long life cycle, about 0.4 mutations are accumulated in each genome in each generation (Drake et al., 1998). Using this estimation, and assuming there are four generations per year, about ten mutations are accumulated in each descendent mouse diploid genome every 6.25 years (Tsang & Chow, 2010). After four years of sibling intercrosses, there is a 90% probability that more than one mutation can be fixed in a particular mouse line (Stevens et al., 2007). To circumvent this problem, the Jackson Laboratory (Bar Harbor, Maine, USA) adopted the Genetic Stability Program to refresh some mouse colonies with cryopreserved embryos once every five generations. This strategy aims at wiping out spontaneous mutations accumulated over time to ensure consistency of the mouse genome composition.
