The extremely rare event, thought to be caused by two sperm cells fertilizing the same egg simultaneously, was last reported in 2007.

To study the fate of stem cells in developing chick embryos, researchers trace their steps over time.

A bright blue stain highlights the sensory nerves of a developing mouse embryo.

Since He Jiankui presented his results at last week’s gene editing summit, researchers have raised concerns about his protocol, calling the procedure “amateurish” and “unconscionable.”

Studying how neural crest cells journey through the embryo, this Caltech developmental biologist has revealed how they form major cell types, including peripheral neurons, bone, and smooth muscle.

Despite a premature and ethically sketchy claim of genome editing in twin girls, an outright prohibition could blunt promising, responsible progress.

He Jiankui, who reportedly edited the genomes of two babies already, broke the news at a conference in Hong Kong.

He Jiankui says he has successfully used CRISPR-Cas9 to tweak the genes of twins born earlier this month. Some independent experts are dubious.

The bipaternal pups died soon after birth, but mice with two mothers grew into fertile adults.