BOX 2.1 Knockout and Knockin Technology
In order to study the relationship between proteins and gene function, scientists now can prevent the manufacturing of a protein by a specific gene. By disabling a gene from a test organism, and then producing descendants that contain two copies of the disabled gene, it is possible to observe the descendants’ development in the absence of a particular protein. This practice, referred to as knockout technology, is an attempt to shut down or turn off a particular gene. Thus far, the mouse has been the mammal in which knockout technology has been most generally applied (University of Guelph, 2001). In essence, a “knockout” organism (e.g., the mouse) is created when an embryo cell (an embryonic stem cell—or ESC—which is a cell that has yet to divide into different tissue cells; NRC, 2002b) is genetically engineered, and then inserted into a developing embryo. The embryo then is inserted surgically into the womb of a host (e.g., a female mouse). Once the embryo has matured, a portion of its stem cells will produce egg and sperm with the knocked-out gene.
A gene also can be altered in function, in contrast to being deleted. When a gene is altered but not shut down, a “targeted mutation” effect is created. This practice is referred to as knockin technology, whereby a life form has an altered gene “knocked” into it (MGD, 2002).