Researchers create female clones from male mice

A Japan-based team used a CRISPR-based method to remove the Y chromosome from male mouse embryos, producing female pups in what researchers describe as sex reversal. The work, published as a bioRxiv preprint and not yet peer reviewed, challenges the assumption that mammalian reproduction always requires both male and female animals.

The method, called Y-CUT, targets a section of the Y chromosome involved in passing it to daughter cells during division. Treated XY embryos were carried by surrogates and born as healthy, fertile XO females with one X chromosome. Researchers then combined the approach with cloning, applying Y-CUT to cloned cells from male mice to generate female clones genetically identical to the original males except for the missing Y chromosome.

The technique could aid conservation by creating females from male samples stored in frozen zoos, including cryopreserved cells and tissues. Scientists cited potential uses in genetically engineered animals and studies of sex chromosomes, but limitations remain: the process still needs hollowed-out egg cells from the same or closely related species, may not help when only females survive, and fertility in XO animals varies beyond mice.