Gene targeting is the use of genetic recombination technology to alter genetic sequences in embryonic stem cells. After a scientist alters the genome, it is possible to introduce the cells to a developing embryo in a procedure called embryonic injection. The embryo will be a chimera, with a mixture of the altered and regular cells. The scientist can use embryos with the target genes in their reproductive cells to develop animals that express, or don't express, the desired gene.
The first step in gene targeting is the identification of a given gene. This requires gene sequencing technology and hypotheses about which areas of the genome contain coding DNA with active genes, and what those genes do. The scientist can engineer a new strand of DNA with a vector to carry it and latch on to the desired section of the genome. This involves the use of complex scientific equipment in a controlled environment.
The new strand of DNA may silence a gene, the first step in creating what is known as knock-out. This is most commonly used in mice, because they are popular for research, and an engineered mouse of this type may be known as a “knock-out mouse.” The organism will not express the given gene, which can result in the development of a genetic disorder or a variation in the physical appearance of the animal. This information can help researchers pinpoint the genes involved in genetic disorders, and learn what individual genes do.
It is also possible to create a knock-in organism, where the gene targeting inserts new DNA. The DNA will express itself and can change the animal's physical traits. In both cases, the researcher usually inserts a tag to be able to identify successful gene targeting. If a scientist wants to know whether inserted DNA is present in a cell, it is possible to check for this tag using DNA sequencing technology. This is important for procedures where researchers want to confirm that they are working with an organism that contains the desired DNA.
Researchers can use gene targeting in a number of applications. These can include research on disease and congenital disorders, as well as experiments to explore the possibilities of gene therapy. In gene therapy, scientists can insert DNA into mature organisms to change the way their genomes express. This technology has the potential to treat a variety of conditions, like enzyme deficiencies, where the inserted DNA can tell the body to start coding the missing enzyme.