In 2005, a husband-and-wife team at Japan’s RIKEN institute ran an experiment with a mouse: clone it, then clone the clone, then clone that clone, and keep going. Dr. Teruhiko Wakayama and Dr. Sayaka Wakayama kept it up for 20 years — through lab moves, a 2011 earthquake, and the pandemic — requiring 30,947 individual cloning attempts to produce 58 successive generations, as summarized by Metacelsus.
Things went smoothly for a while. An interim report in 2013 showed 25 healthy generations with no decline in cloning efficiency or mouse health. But mutations were quietly accumulating. By generation 57, the mice carried over 3,400 single-base DNA changes compared to the original — a mutation rate 3.1 times higher than natural reproduction in the same mouse strain. Sexually reproducing animals can shake off harmful mutations through recombination, where chromosomes shuffle and bad copies get discarded. Clones have no such mechanism, so every error sticks.
The bigger problems were structural. Somewhere between generations 25 and 45, an entire X chromosome vanished and never came back. Chromosomal deletions, inversions, and translocations piled up alongside the point mutations. By generation 58, the cells simply wouldn’t produce viable clones anymore, and the project ended. The mice that were born at every stage lived normal lifespans — the process didn’t produce sickly animals, just increasingly fragile DNA that eventually couldn’t survive the cloning procedure itself.
Hellbound and Down 