Ishiuchi and his colleague Shogo Matoba at the Riken Bio Resource Research Center have engineered a CRISPR‑based method to cut out the Y chromosome, allowing them to create female clones of male mice. They hope the technique could aid conservation when very few members of a species remain.

The first widely known clone, Dolly the sheep, was positively produced in 1996 by transferring an adult mammary cell nucleus into an enucleated egg. Cloning pets has followed, with companies charging tens of thousands of dollars to replicate beloved animals. Critics, such as bioethicist Jessica Pierce, have called the practice an exploitation of the canine underclass.

Conservation cloning uses “frozen zoos.” The San Diego Zoo holds cells from 1,300 species that have been cryopreserved. Scientists have produced clones of near‑extinct animals like the black‑footed ferret and the Pyrenean ibex—only one of the 439 embryos succeeded, but the lone female died minutes after birth.

Colossal Biosciences is targeting long‑extinct species such as the thylacine and woolly mammoth, while a startup has proposed brainless human clones that could serve as organ donors. Such promises stir excitement and nervousness about the future of cloning technology.