If you think cloning humans is controversial, science is about to throw another curve ball: 3-parent embryos.
Researchers have produced human embryos containing DNA from three people, a biotechnological proof-of-principle with profound medical and ethical implications.
To accomplish this, chromosomes were taken from one zygote — the single cell formed when sperm and egg fuse — and put into a zygote stripped of its original chromosomes, but left with its original mitochondria, which provide each human cell with energy.
As they grew, the resulting embryos contained so-called nuclear DNA — the 25,000 genes responsible for physical and developmental traits — from two traditional parents, and mitochondrial DNA from a third.
The technique is a subtle form of genetic engineering, which many people consider taboo, and raises other ethical dilemmas. It could also allow parents whose progeny would otherwise suffer from deadly mitochondrial diseases to have healthy children.