WHAT HAPPENS WHEN YOU CLONE MICE FOR 20 YEARS STRAIGHT?

Summary from the TLDR newsletter

Two scientists conducted a study over 20 years where they cloned generations of mice to see what would happen. The researchers created a total of 58 generations before the project ended - the mouse cells just wouldn't make clones. This took 30,947 individual attempts due to the low efficiency of cloning technology. There was a steady accumulation of mutations over the generations, and an entire X chromosome was lost at some point between generations 25 and 45, and never regained. The various other chromosomal deletions, inversions, and translocations added to the reasons why the cloning process failed after 58 generations.