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Girl mice grew balls after a one-letter DNA change

Ellsworth Toohey
Apr 10, 2026
∙ Paid

Mickey Mouse in The Gallopin’ Gaucho, c. 1928

Swap one letter in a girl mouse’s DNA and she grows testes. Researchers at Bar-Ilan University in Israel edited a small stretch of what scientists used to call “junk DNA,” the vast majority of the genome that doesn’t build proteins but tells other genes when to turn on or off. This particular switch, describe…

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