Wanting to have children who follow in one’s footsteps is an understandable desire. But a coming article in the journal Fertility and Sterility offers a fascinating glimpse into how far some parents may go to ensure that their children stay in their world — by intentionally choosing malfunctioning genes that produce disabilities like deafness or dwarfism. The article reviews the use of preimplantation genetic diagnosis, or P.G.D., a process in which embryos are created in a test tube and their DNA is analyzed before being transferred to a woman’s uterus. In this manner, embryos destined to have, for example, cystic...