Scheme illustrating the effect of spontaneous mutations and genetic drift responsible for the divergence of animal subcolonies bred independently (Figure from Montoliu and Whitelaw, Transgenic Research, 2018, online May 31).
Bruce Whitelaw (The Roslin Institute, Edinburgh, Scotland, UK) and I, we have just published a commentary in the scientific journal Transgenic Research discussing the case of the Nature Methods paper by Schaefer et al. 2017 who initially reported the identification of numerous off-target sites altered after a genome-editing experiment in vivo, in mice. This paper has recently been retracted by the journal (March 30). As indicated by the authors in this commentary: “The most plausible explanation for the vast majority of the reported unexpected mutations were the expected underlying genetic polymorphisms that normally accumulate in two different colonies of the same mouse strain which occur as a result of spontaneous mutations and genetic drift. Therefore, the reported mutations were most likely not related to CRISPR-Cas9 activity.“