Overview
- Researchers in Japan serially cloned a mouse line for 58 generations, and by the last round the newborns died soon after birth as success rates had fallen since the mid‑20s generations.
- Genome sequencing showed more than 70 new mutations per generation, about three times the rate in naturally bred mice, with large DNA changes building after around generation 27, including the loss of an X chromosome.
- The damage often surfaced in reproduction and development, with smaller litters and oversized placentas, even though many clones looked normal and some lived typical lifespans.
- The team used somatic cell nuclear transfer, which puts a nucleus from a body cell into an egg with its own DNA removed, a process that skips the germline’s usual DNA repair and reshuffling.
- Experts disagree on the main cause, with Teruhiko Wakayama citing damage from the transfer step and Shoukhrat Mitalipov pointing to flaws in donor cells, and they propose screening donor cells, fixing harmful variants with gene editing, and exploring gentler transfer methods as farms, conservation groups, and de‑extinction projects weigh the risks.