While social conservatives of a certain stripe are fretting about the possibility that gay marriage might open the door to other unorthodox family arrangements, a British research team at Newcastle University is on the verge of assembling babies with three biological parents. These embryos would use the genetic material from the nucleus of an ordinary fertilized egg (the yolk) but borrow a hollowed-out egg (the white) from another woman. The second woman's egg would still contain her mitochondria, which have genetic material of their own.
The aim is to prevent rare, but serious, mitochondrial diseases. There are currently no treatments for this family of diseases, which are inherited matrilineally. A child born using the new process would have DNA from all three parents. Heather could now have two mommies and a daddy. (Most of the genetic material would be from the parents of the first fertilized egg, since mitochondria contain only a smidge of genetic material.)
A few three-parented children already walk among us, the product of some work done in the late 1990s. But the next wave of tripartite kids won't hold U.S. passports. The Food and Drug Administration has banned the process, out of fear that mitochondrial mixing will cause unspecified birth defects.