Designer babies. Conceptual computer artwork of a hand lens examining babies in a molecule of DNA (deoxyribonucleic acid). This represents designing a baby by altering its DNA. The babies are joining the twisting strands that form the DNA helix. They have replaced the nucleotide bases (still seen at left and right) that normally join the strands. It is the sequence of these bases that is the genetic code for an organism's inherited characteristics. Genetically modified (GM) plants and animals have been engineered, but human designing faces ethical and practical problems. GM humans may be healthier and more intelligent.