This is a hugely controversial topic, with people arguing strongly both for and against.
What do you think about human organs grown in animals? Would you accept such an organ to save either your own or a family member's life?
Human organs are being grown in animals in the US in a controversial technique that is likely to be approved by the Home Office this week. Dozens of pigs and sheep have been implanted with embryos which have both animal and human DNA. It is hoped that when the hybrid animals are fully grown, their organs will be fully transplantable into patients without rejection because they carry human genetic material.