Is the moral debate over? Ten years ago, experts were divided over allowing "three-parent" babies. Now, the first babies have been born healthy.
Three-parent babies born disease-free
Chance of a normal life: The mitochondria are known as "the powerhouse of the cell" — but when somebody has mitochondrial disease, this power is missing. Glossary
Miracle - Something amazing or wonderful. It is a very unusual event.
DNA - Deoxyribonucleic acid is the material in an organism that carries genetic information.
Cells - The smallest bit of a plant or animal that can live on its own.
Fertilised - Join an egg with male reproductive material to cause new life to grow.
Embryo - A fertilised egg that is developing into a foetus.
Legal - Something that is legal is allowed by the law.