From the Washington Post:

British lawmakers stepped into the complex crossroads of science and fertility Tuesday with debate on becoming the first country to allow so-called “three-parent” babies using genetic material from a mother, father and a female donor.
The vote, expected later in the day, is over whether to approve in-vitro procedures to avoid passing along inherited and incurable diseases from mitochondrial DNA, which is carried from mother to child.
Supporters say it would offer hope to families who would otherwise risk passing along diseases such as muscular dystrophy to their offspring. But a wide range of critics question the ethics of the proposals, saying it would be another step toward creating “designer babies.”