Britain has become the first country in the world to allow the creation of babies with DNA from three people, after MPs voted for the controversial procedure.
The treatment is known as "three-parent" in vitro fertilisation (IVF) because the babies, born from genetically modified embryos, would have DNA from a mother, a father and from a female donor.
It is designed to help families with mitochondrial diseases, incurable conditions passed down the maternal line that affect around one in 6500 children worldwide.
It is fiercely disputed by some religious groups and other critics, with fears that people could start "designing" their babies.
The process involves intervening in the fertilisation process to remove mitochondria, which act as tiny energy-generating batteries inside cells and which, if faulty, can cause inherited conditions such as fatal heart problems, liver failure, brain disorders, blindness and muscular dystrophy.
Mitochondrial DNA is separate from DNA found in the cell nucleus and does not affect human characteristics such as hair or eye colour, appearance or personality traits.
Professor Julian Savulescu, from the Oxford Centre for Practical Ethics, spoke to John, and says this is definitely NOT the start of so-called "designer babies":