“[O]ur results align closely with Muller’s ratchet theory,” they add. “This model predicts that in asexual lineages, deleterious mutations inevitably accumulate, ultimately producing mutational meltdown and extinction.”<\/p>\n
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Since the first mammal was cloned in the mid-1990s, famously called Dolly the Sheep<\/a>, scientists have learned a great deal about the whole process<\/a>, and how to recreate an animal using very few cells.<\/p>\n Some conservationists hope<\/a> that the practice can one day help us bring back species from the brink of extinction, and a few celebrities have even started cloning their pets<\/a>.<\/p>\n While this might work for a while, over time, as clones are re-cloned and then re-cloned again, dangerous mutations can accumulate in the genome. How long this takes to kill a creature is unknown, and scientists in Japan wanted to find out using mice.<\/p>\n For the team’s first 25 cloning attempts, the re-cloned mice looked no different to the original genetic donor. In fact, success rates improved with each generation of clones, leading the authors to suspect<\/a> “it may be possible to reclone animals indefinitely”.<\/p>\n But then, something changed. The success rates of the cloned mice gradually declined before suddenly coming to an end.<\/p>\n It seemed that the mice had somehow lost their ability to efficiently eliminate chromosomal abnormalities and coding mutations.<\/p>\n Loss of the X chromosome became a prominent problem after the 25th generation of clones, and the frequency of deleterious mutations nearly doubled by the 57th generation.<\/p>\n Even those carrying mutations, however, lived normal lifespans \u2013 until generation 58, that is.<\/p>\n “Although serial cloning could not continue beyond the 58th generation (G58), the re-cloned mice remained healthy except G58, raising the possibility that subsequent generations could be produced via sexual reproduction,” the authors suggest<\/a>.<\/p>\n To test that idea, the team took female mice from the 20th, 50th, and 55th generations and mated them with normal male mice. The 20th-generation clones had similar litter sizes to control mice, but 50th- and 55th-generation clones had dramatically smaller litters.<\/p>\n Related: These Baby Ferrets Are The First to Be Born From a Clone<\/a><\/strong><\/p>\n Still, when those offspring lineages produced grandchildren of the clones with normal mice, their litter sizes increased again to a healthy number.<\/p>\n The findings suggest that mammal species can be surprisingly tolerant of genetic mutations, remaining fit and able to reproduce even in the face of widespread genetic alterations.<\/p>\n The study, the authors say, reaffirms<\/a> “the evolutionary inevitability that sexual reproduction is indispensable for the long-term survival of mammalian species”.<\/p>\n![\"YouTube](\"https:\/\/www.europesays.com\/us\/wp-content\/uploads\/2026\/03\/1774387216_513_0.jpg\")
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