There are three types of human genetic engineering: somatic, germline and cloning. Somatic engineering adds genes to body cells. Germline engineering adds genes to human eggs, embryos or sperm, and cloning creates a copy of an organism.
The genes of living cells can be altered by inserting a new gene into a virus-like organism. This organism is then allowed to enter cells and insert a new gene into the genome. This procedure is performed by either somatic or germline engineering.
Somatic engineering targets specific genes of the body in specific organs and tissues, and it does not affect the genes in the eggs or sperm. This type of genetic engineering treats or cures existing conditions, but it does not alter an individual’s entire genetic makeup.
Germline engineering targets the genes in eggs, sperm or embryos during very early stages of their development. All the cells in embryos are genetically affected. This type of modification causes more controversy because it renders permanent gene changes. Future generations can inherit the changes from germline engineering, whereas somatic genetic modifications cannot be inherited.
Finally, there is cloning, which can be performed in three ways. DNA cloning is when a DNA fragment is transferred from one organism to a self-replicating genetic element so that the DNA can replicate itself in a foreign host cell. Reproductive cloning, however, creates an organism with the same nuclear DNA as another currently or previously existing organism, such as Dolly the sheep. Finally, therapeutic cloning, or embryo cloning, describes the production of human embryos for research.