Perhaps you recall from your high school biology class that mitochondria are like batteries in a cell, giving it energy. Some kids, though, are born with malfunctioning mitochondria that can cause blindness, deafness or other serious diseases. But there may be a way to prevent this birth defect with the three parent child.

How it works is quite straightforward. Mitochondria have their own genomes and float in the cytoplasm outside the cell nucleus and are passed on by the mother to her offspring. Working with women who have defective mitochondria, scientists removed the nucleus from one of their eggs and placed it into a donor egg. This donor egg had its nucleus removed and carries healthy mitochondria.

So now the new egg carries the mother's nucleus and the donor's healthy mitochondria. Then the egg is fertilized with the father's sperm.

About five years ago, scientists tried this on primates and the four monkeys born remain healthy to this day. In recent studies with human eggs, about half grew to a one-hundred cell stage called a blastocyst, which is optimal for implanting in the uterus. But that hasn't been tried yet. Children born of this method would carry the donor's healthy mitochondria and pass on this third parent's mitochondria to their own children.

Medical ethicists are alarmed by this permanent genetic alteration without proof that it's safe. Plus - are donors considered a parent even though their genetic contribution is just 1%? And should the children be told? Ethicists believe that this is flirting with designer babies, where parents can choose eye color or intelligence, for example.

But to parents whose children could be born with lifelong mitochondrial defects, these arguments may seem off-base.