Unlike the somatic cell gene therapy being used in experiments today, germ-line gene therapy would affect an individual's descendants, because it would change a person's eggs or sperm. Because every cell in the human body descends from that fertilized egg, every cell would have the transplanted gene. This would be a far more effective way of transferring genes than those used in current somatic cell gene therapies, where genes transferred into children or adults usually enter only a small portion of the body's cells and eventually cease to function. Germ-line therapy on early embryos could become an alternative to prenatal diagnosis and selective abortion. Once a genetic defect was repaired, the repair would not have to be done over again on a person's descendants.
Artificial chromosomes are already here.
Human artificial chromosomes have also been developed by Dr. Leroy Hood of the University of Washington, Seattle. The basic technology for germ-line therapy already exists, according to Drs. This would presumably enable scientists to correct their mistakes. The downside of germline gene therapy is that it could cause permanent and unforeseen changes in what it means to be human. In other words, it could lead to unintentional evolution in which our descendants are so unlike us that they do not even recognize us as fully human.