http://www.sciencemag.org/news/2018/06/little-piece-dna-makes-girls-boys

The XY chromosome combination defines a boy, but a tiny piece of regulatory DNA makes it happen.

What if you could flip a single DNA switch and make a world of only women? That sci-fi vision is unlikely to become reality anytime soon, yet such a switch—one near the gene that prompts the development of male body parts in embryos—has just been discovered in mice. The finding could help explain why some human babies with a male chromosome are born female, and the “groundbreaking” method used to unearth this so-called enhancer might one day identify similar DNA switches that are key to a variety of diseases.