It takes one man and one woman to make a baby, right? Well, no. New advances in genetic engineering have biologists, politicians and ethicists questioning how babies are made.

Ever since the dawn of in vitro fertilization (IVF) — in which a mother's egg and a father's sperm are combined medically in a lab before being implanted into the mother — many have wondered how far medicine will go to create human babies. A new advancement called mitochondrial replacement technique, or MRT, may soon redefine our understanding of genetics by making it possible to create one baby from three parents.

The role of MRT is not to create designer babies with enhanced genetic traits but to allow a mother to pass on her genetic material to her child without also passing on a mitochondrial defect that could lead to a rare but fatal disease.

Here's how it works: Inside a mother's egg, there are more than 23,000 genes in the nucleus that determine things like the baby's hair color, eye color, size and many other traits. Outside the nucleus, there are about 37 genes in the mitochondria that influence the energy produced by the cell. When there is a flaw in the mitochondria, it can lead to rare but fatal diseases such as Leigh's disease, Barth syndrome and progressive infantile poliodystrophy. Mitochondrial defects are also linked to Parkinson's disease, deafness, blindness, diabetes and epilepsy. According to the United Mitochondrial Disease Foundation, between 1,000 and 4,000 babies are born with mitochondrial diseases every year.

How could MRT be used to prevent these diseases? The technique involves taking the nucleus from the egg of the mother and implanting into a donor egg that has been stripped of everything but its healthy mitochondria. The new egg is then fertilized by the father before it is implanted into the mother. In this way, a mother can pass on almost all of her genetic material to her child except for her faulty mitochondria. The mitochondrial genes from the donor egg make up less than 1 percent of the genes of the baby.

This video does an excellent job of explaining the procedure:

Still, there is no question that MRT raises serious questions about the role of science in the creation of babies. For starters, the children born via this method will technically have the ancestry of three parents. In addition, researchers have no way of knowing for sure how the DNA from the genetically altered eggs will develop over time. Will the mitochondrial DNA from one egg be able to communicate with the nucleic DNA from another? Could this lead to a host of new diseases and conditions? And finally, would MRT open the door for other forms of genetic engineering in humans?

These are all valid questions that genetics, ethicists, politicians and government officials have been struggling to answer. Last year, the Food and Drug Administration asked the Institute of Medicine (now part of the National Academies of Sciences, Engineering and Medicine) to review MRT and its ethical implications. British officials have already approved the use of the technique.

Early this year the panel released their conclusion — that MRT be approved for clinical trials — but only under certain conditions. First, the panel recommended that the technique only be used to prevent the transmission of mitochondrial diseases, not to help older women overcome fertility issues (another potential benefit of MRT). Second, the technique should only be used to create male embryos. Mitochondria are passed on only in the mother's eggs, not the father's sperm. Thus if there are future issues that arise from the technique, they would not be passed onto future generations.

However, despite the panel's conclusion, the FDA still may not be able to move forward with MRT because a budget bill passed in Congress last year prohibits the agnecy from considering applications for research projects that allow “the creation of a human embryo or embryos for research purposes.” As MRT falls under this definition, the FDA cannot even consider applications until a new budget is passed at the end of this year.