Genetic engineering, the artificial manipulation, modification, and recombination of DNA or other nucleic acid molecules in order to modify an organism or population of organisms.

Initially referred to various techniques used for the modification or manipulation of organisms through the processes of heredity and reproduction. Embraced both artificial selection and all the interventions of biomedical techniques, among them artificial insemination, fertilization (e.g., “test- tube” babies), , and gene manipulation. In 20th century, specifically used to the methods of recombinant DNA technology (or gene cloning), in which DNA molecules from two or more sources are combined either within cells or in vitro and are then inserted into host organisms in which they are able to propagate. The possibility for recombinant DNA technology emerged with the discovery of restriction in 1968 by Swiss microbiologist . The following year American microbiologist Hamilton O. Smith purified so- called type-II restriction enzymes, which were found to be essential to for their ability to cleave a specific site within the DNA (as opposed to type-I restriction enzymes, which cleave DNA at random sites). Drawing on Smith’s work, American molecular biologist helped advance the technique of DNA recombination in 1970–71 and demonstrated that type-II enzymes could be useful in genetic studies. Genetic engineering based on recombination was pioneered in 1973 by American biochemists Stanley N. Cohen and Herbert W. Boyer, who were among the first to cut DNA into fragments, rejoin different fragments, and insert the new genes into E. coli bacteria, which then reproduced. Process And Techniques Most recombinant DNA technology involves the of foreign genes into the of common laboratory strains of bacteria. Plasmids are small rings of DNA; they are not part of the bacterium’s chromosome (the main repository of the organism’s genetic information) They are capable of directing protein synthesis, and, like chromosomal DNA, they are reproduced and passed on to the bacterium’s progeny. By incorporating foreign DNA (for example, a mammalian gene) into a bacterium, researchers can obtain an almost limitless number of copies of the inserted gene. If the inserted gene is operative (i.e., if it directs protein synthesis), the modified bacterium will produce the protein specified by the foreign DNA. A subsequent generation of genetic engineering techniques that emerged in the early 21st century centered on gene editing. Gene editing, based on a technology known as CRISPR-Cas9 ["Clusters of Regularly Interspaced Short Palindromic Repeats." It is a specialized region of DNA with two distinct characteristics: the presence of repeats and spacers. Repeated sequences of — the building blocks of DNA — are distributed throughout a CRISPR region. Spacers are bits of DNA that are interspersed among these repeated sequences.], allows researchers to customize a living organism’s genetic sequence by making very specific changes to its DNA. Gene editing has a wide array of applications, being used for the genetic modification of crop plants and livestock and of laboratory model organisms (e.g., mice). The correction of genetic errors associated with disease in animals suggests that gene editing has potential applications in for humans. Applications Genetic engineering has advanced the understanding of many theoretical and practical aspects of gene function and organization. Through recombinant DNA techniques, bacteria have been created that are capable of synthesizing human , human , alpha interferon, a , and other medically useful substances. Plants may be genetically adjusted to enable them to fix nitrogen, and genetic diseases can possibly be corrected by replacing dysfunctional genes with normally functioning genes. Nevertheless, special concern has been focused on such achievements for fear that they might result in the introduction of unfavorable and possibly dangerous traits into microorganisms that were previously free of them e.g., resistance to antibiotics, production of toxins, or a tendency to cause disease. Likewise, the application of gene editing in humans has raised ethical concerns, particularly regarding its potential use to alter traits such as intelligence and beauty. Genetic engineering has many applications to that include; ❑Manufacturing of drugs e.g. human insulin etc., ❑Creation of model animals that mimic human conditions and gene therapy. ❑Mouse hybridomas, cells fused together to create monoclonal , have been adapted through genetic engineering to create human monoclonal antibodies. ❑In 2017, genetic engineering of chimeric antigen receptors on a patient's own T-cells was approved by the U.S. FDA as a treatment for the cancer acute lymphoblastic leukemia. ❑Genetically engineered are being developed that can still confer immunity, but lack the infectious sequences. Genetic engineering is also used to create animal models of human diseases. Genetically modified mice are the most common genetically engineered animal model. They have been used to study and model cancer (the ), obesity, heart disease, , arthritis, substance abuse, anxiety, aging and Parkinson disease. Potential cures can be tested against these mouse models. Also genetically modified pigs have been bred with the aim of increasing the success of pig to human organ transplantation.

Gene therapy is the genetic engineering of humans, generally by replacing defective genes with effective ones. Clinical using somatic gene therapy has been conducted with several diseases, including X-linked SCID, chronic lymphocytic leukemia (CLL), and Parkinson's disease. In 2012, Alipogene tiparvovec became the first gene therapy treatment to be approved for clinical use. In 2015 a was used to insert a healthy gene into the skin cells of a boy suffering from a rare skin disease, epidermolysis bullosa, in order to grow, and then graft healthy skin onto 80 percent of the boy's body which was affected by the illness. Germline gene therapy would result in any change being inheritable, which has raised concerns within the scientific community. In 2015, CRISPR was used to edit the DNA of non- viable human embryos, leading scientists of major world academies to call for a moratorium on inheritable human edits. There are also concerns that the technology could be used not just for treatment, but for enhancement, modification or alteration of a human beings' appearance, adaptability, intelligence, character or behavior. The distinction between cure and enhancement can also be difficult to establish. In November 2018, He Jiankui announced that he had edited the of two human embryos, to attempt to disable the CCR5 gene, which codes for a receptor that HIV uses to enter cells. He said that twin girls, Lulu and Nana, had been born a few weeks earlier. He said that the girls still carried functional copies of CCR5 along with disabled CCR5 (mosaicism) and were still vulnerable to HIV. The work was widely condemned as unethical, dangerous, and premature. Researchers are altering the genome of pigs to induce the growth of human organs to be used in transplants. Scientists are creating "gene drives", changing the genomes of mosquitoes to make them immune to malaria, and then looking to spread the genetically altered mosquitoes throughout the mosquito population in the hopes of eliminating the disease.