Revealing the limitations of cloning, researchers who repeatedly cloned mice for two decades have discovered that such serial duplication triggers grave genetic mutations that accumulate over the generations and ultimately become fatal. A total of 1,206 cloned laboratory mice were generated by the scientists from a single female donor mouse from 2005 to 2025 in research conducted in Japan. There were no outward signs of trouble through the first 25 generations, but mutations subsequently began piling up until becoming fatal. The 58th generation of clones, burdened by mutations but with no visible physical abnormalities, died within a few days of birth.
The research contradicted the notion that clones are identical copies of the original donor animal and disproved the idea that cloning using current technology could be carried out indefinitely with no ill effects.