Last week members of the British House of Commons passed a bill legalizing mitochondrial DNA transfers--a process that combines three different sets of DNA to create an embryo. That means one day, it could be possible for children in the United Kingdom to have DNA from three parents.

Although the bill cleared the Commons by a vote of 382-128, it needs approval from the House of Lords before it can be enacted. Even with overwhelming government support, however, debate about the procedure is far from over.

Supporters argue there's a need for three-person in vitro fertilization: Mothers can pass along potentially life-threatening diseases through their mitochondrial DNA. Mitochondria are the powerhouses of cells, and they contain their own set of DNA with 37 genes. Once a sperm fertilizes an egg, the father's mitochondrion dissolve and the mother's mitochondrial DNA sticks around. Mitochondrial DNA don't carry information about specific traits--all of that information comes from the nucleus.