Genetic engineering,
recombinant DNARecombinant DNA is a form of DNA that does not exist naturally, which is created by combining DNA sequences that would not normally occur together...
technology,
genetic modification/manipulation (GM) and
gene splicing are terms that apply to the direct manipulation of an
organismIn biology, an organism is any living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homeostasis as a stable whole...
's
geneA gene is the basic unit of heredity in a living organism. All living things depend on genes. Genes hold the information to build and maintain their cells and pass genetic traits to offspring...
s. Genetic engineering is different from traditional
breedingBreeding is the producing of offspring, usually animals or plants:* Breeding in the wild, the natural process of reproduction in the animal kingdom* Animal husbandry, through selected specimens such as dogs, horses, and rabbits...
, where the organism's genes are manipulated indirectly. Genetic engineering uses the techniques of
molecular cloningMolecular cloning refers to the procedure of isolating a defined DNA sequence and obtaining multiple copies of it in vivo. Cloning is frequently employed to amplify DNA fragments containing genes, but it can be used to amplify any DNA sequence such as promoters, non-coding sequences, chemically...
and
transformationIn molecular biology, transformation is the genetic alteration of a cell resulting from the uptake, genomic incorporation, and expression of foreign genetic material ....
to alter the structure and characteristics of genes directly. Genetic engineering techniques have
found some successes in numerous applications. Some examples are in improving crop technology, the manufacture of synthetic human
insulinInsulin is a hormone that has extensive effects on metabolism and other body functions, such as vascular compliance. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle, and stopping use of fat as an energy...
through the use of modified
bacteriaThe bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, the manufacture of
erythropoietinErythropoietin, or its alternative erythropoetin or EPO, is a glycoprotein hormone that controls erythropoiesis, or red blood cell production...
in hamster
ovaryThe ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in females are homologous to testes in males, in that they are both gonads and endocrine glands.-Human anatomy:...
cells, and the production of new types of experimental mice such as the
oncomouseThe OncoMouse or Harvard mouse is a type of laboratory mouse that has been genetically modified using modifications designed by Philip Leder and Timothy A. Stewart of Harvard University to carry a specific gene called an activated oncogene. The activated oncogene significantly increases the...
(cancer mouse) for research.
The term "genetic engineering" was coined in
Jack WilliamsonJohn Stewart Williamson , who wrote as Jack Williamson was a U.S. writer often referred to as the "Dean of Science Fiction" following the death in 1988 of Robert A...
's
science fictionScience fiction is a genre of fiction. It differs from fantasy in that, within the context of the story, its imaginary elements are largely possible within scientifically-established or scientifically-postulated laws of nature...
novelA novel is a long narrative in literary prose. The genre has historical roots both in the fields of the medieval and early modern romance and in the tradition of the novella. The latter supplied the present generic term in the late 18th century....
Dragon's Island, published in 1951, two years before
James WatsonJames Watson is the name of:*James Watson , British film and television actor*James Watson , United States Senator from New York...
and
Francis CrickFrancis Harry Compton Crick OM FRS , was a British molecular biologist, physicist, and neuroscientist, and most noted for being one of two co-discoverers of the structure of the DNA molecule in 1953, together with James D. Watson. He, James D...
showed that
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information...
could be the medium of transmission of genetic information.
Engineering
There are a number of ways through which genetic engineering is accomplished. Essentially, the process has five main steps.
- Isolation of the genes of interest
- Insertion of the genes into a transfer vector
In molecular biology, a vector is a DNA molecule used as a vehicle to transfer foreign genetic material into another cell. The four major types of vectors are plasmids, bacteriophages and other viruses, cosmids, and artificial chromosomes...
- Transfer of the vector to the organism to be modified
- Transformation
In molecular biology, transformation is the genetic alteration of a cell resulting from the uptake, genomic incorporation, and expression of foreign genetic material ....
of the cells of the organism
- Selection of the genetically modified organism (GMO) from those that have not been successfully modified
Isolation is achieved by identifying the gene of interest that the scientist wishes to insert into the organism, usually using existing knowledge of the various functions of genes. DNA information can be obtained from cDNA or
gDNAGenomic deoxyribonucleic acid is often abbreviated as gDNA. The genome of an organism is the biological information of heredity which is passed from one generation of organism to the next. That genome is transcribed to produce RNAs, which are necessary for the function of the organism...
libraries, and amplified using PCR techniques. If necessary, i.e. for insertion of eukaryotic genomic DNA into prokaryotes, further modification may be carried out such as removal of introns or ligating prokaryotic promoters.
Insertion of a gene into a vector such as a
plasmidA plasmid is an extra-chromosomal DNA molecule separate from the chromosomal DNA which is capable of replicating independently of the chromosomal DNA. In many cases, it is circular and double-stranded...
can be done once the gene of interest is isolated. Other vectors can also be used, such as viral vectors,
bacterial conjugationBacterial conjugation is the transfer of genetic material between bacteria through direct cell-to-cell contact, or through a bridge-like connection between the two cells...
, liposomes, or even direct insertion using a
gene gunA gene gun or a biolistic particle delivery system, originally designed for plant transformation, is a device for injecting cells with genetic information. The payload is an elemental particle of a heavy metal coated with plasmid DNA...
.
Restriction enzymeA restriction enzyme is an enzyme that cuts double-stranded or single stranded DNA at specific recognition nucleotide sequences known as restriction sites. Such enzymes, found in bacteria and archaea, are thought to have evolved to provide a defense mechanism against invading viruses...
s and ligases are of great use in this crucial step if it is being inserted into prokaryotic or viral vectors.
Daniel NathansDaniel Nathans was an American microbiologist.He was born in Wilmington, Delaware, the last of nine children born to Russian Jewish immigrant parents. During the Great Depression his father lost his small business and was unemployed for a long period of time...
and Hamilton Smith received the 1978
Nobel PrizeThe Nobel Prize is a Sweden-based international monetary prize. The award was established by the 1895 will and estate of Swedish chemist and inventor Alfred Nobel. It was first awarded in Physics, Chemistry, Physiology or Medicine, Literature, and Peace in 1901...
in Physiology or MedicineThe Nobel Prize in Physiology or Medicine is awarded once a year by the Swedish Karolinska Institute. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895, awarded for outstanding contributions in Physics, Chemistry, Literature, Peace, and Physiology or Medicine...
for their isolation of
restriction endonucleasesA restriction enzyme is an enzyme that cuts double-stranded or single stranded DNA at specific recognition nucleotide sequences known as restriction sites. Such enzymes, found in bacteria and archaea, are thought to have evolved to provide a defense mechanism against invading viruses...
.
Once the vector is obtained, it can be used to
transform the
target organism. Depending on the vector used, it can be complex or simple. For example, using raw DNA with gene guns is a fairly straightforward process but with low success rates, where the DNA is coated with molecules such as gold and fired directly into a cell. Other more complex methods, such as
bacterial transformationIn molecular biology, transformation is the genetic alteration of a cell resulting from the uptake, genomic incorporation, and expression of foreign genetic material ....
or using viruses as vectors have higher success rates.
After transformation, the
GMO can be
selected from those that have failed to take up the vector in various ways. One method is screening with DNA probes that can stick to the gene of interest that was supposed to have been transplanted. Another is to package genes conferring resistance to certain chemicals such as antibiotics or herbicides into the vector. This chemical is then applied ensuring that only those cells that have taken up the vector will survive.
Applications
The first genetically engineered medicine was synthetic human
insulinInsulin is a hormone that has extensive effects on metabolism and other body functions, such as vascular compliance. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle, and stopping use of fat as an energy...
, approved by the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
Food and Drug AdministrationThe Food and Drug Administration is a Government agency of the United States Department of Health and Human Services and is responsible for regulating and supervising the safety of foods, tobacco products, dietary supplements, Medication drugs, vaccines, Biopharmaceutical, blood transfusion,...
in 1982. Another early application of genetic engineering was to create human growth hormone as replacement for a compound that was previously extracted from human
cadaverA cadaver is a dead human body.Cadaver may also refer to:* Cadaver tomb, tomb featuring an effigy in the form of a decomposing body* Cadaver , a video game* Cadaver , a Norwegian death metal band...
s. In 1987 the FDA approved the first genetically engineered
vaccineA vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains a small amount of an agent that resembles a microorganism...
for humans, for hepatitis B. Since these early uses of the technology in medicine, the use of GM has gradually expanded to supply a number of other drugs and vaccines.
One of the best-known applications of genetic engineering is the creation of GMOs for food use (genetically modified foods); such foods resist insect pests, bacterial or fungal infection, resist herbicides to improve yield, have longer freshness than otherwise, or have superior nutritional value.
In materials science, a genetically modified virus has been used to construct a more environmentally friendly lithium-ion battery.
A new type of slowly growing artform is being established via gene engineering and manipulation.
BioartBioArt is an art practice in which the medium is living matter and the works of art are produced in laboratories and/or artists’ studios. The tool is biotechnology, which includes such technologies as genetic engineering, tissue culture and cloning...
, an artistic form, uses gene engineering to create new art forms that both educate the public about genetics and create living artforms.
Genetic engineering and research
Although there has been a revolution in the biological sciences in the past twenty years, there is still a great deal that remains to be discovered. The completion of the sequencing of the
human genomeThe human genome is the genome of Homo sapiens, which is stored on 23 chromosome pairs. Twenty-two of these are autosomal chromosome pairs, while the remaining pair is sex-determining...
, as well as the genomes of most agriculturally and scientifically important animals and plants, has increased the possibilities of genetic research immeasurably. Expedient and inexpensive access to comprehensive genetic data has become a reality with billions of sequenced
nucleotideNucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides play central roles in metabolism...
s already online and annotated.
- Loss of function experiments, such as in a gene knockout
A gene knockout is a genetic technique in which an organism is engineered to carry genes that have been made inoperative . Also known as knockout organisms or simply knockouts, they are used in learning about a gene that has been sequenced, but which has an unknown or incompletely known function...
experiment, in which an organism is engineered to lack the activity of one or more genes. This allows the experimenter to analyze the defects caused by this mutationIn biology, a mutation is a randomly derived change to the nucleotide sequence of the genetic material of an organism.Mutations can be caused by copying errors in the genetic material during cell division, or by exposure to mutagens , or can be induced by the organism itself, by cellular processes...
, and can be considerably useful in unearthing the function of a gene. It is used especially frequently in developmental biologyDevelopmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis," which is the process that gives rise to tissues, organs and anatomy.Developmental biology is that...
. A knockout experiment involves the creation and manipulation of a DNA construct in vitroA procedure performed in vitro is performed not in a living organism but in a controlled environment, such as in a test tube or Petri dish...
, which, in a simple knockout, consists of a copy of the desired gene, which has been slightly altered such as to cripple its function. The construct is then taken up by embryonic stem cells, wherein the engineered copy of the gene replaces the organism's own gene. These stem cells are injected into blastocystThe blastocyst is a structure formed in the early embryogenesis of mammals, after the formation of the morula, but before implantation. It possesses an inner cell mass , or embryoblast, which subsequently forms the embryo, and an outer layer of cells, or trophoblast, which later forms the placenta...
s, which are implanted into surrogate mothers. Another method, useful in organisms such as DrosophilaDrosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
(fruitfly), is to induce mutations in a large population and then screen the progeny for the desired mutation. A similar process can be used in both plants and prokaryotes.
- Gain of function experiments, the logical counterpart of knockouts. These are sometimes performed in conjunction with knockout experiments to more finely establish the function of the desired gene. The process is much the same as that in knockout engineering, except that the construct is designed to increase the function of the gene, usually by providing extra copies of the gene or inducing synthesis of the protein more frequently.
- Tracking experiments, which seek to gain information about the localization and interaction of the desired protein. One way to do this is to replace the wild-type gene with a 'fusion' gene, which is a juxtaposition of the wild-type gene with a reporting element such as Green Fluorescent Protein
The green fluorescent protein is protein composed of 238 amino acids , which exhibits bright green fluorescence when exposed to blue light. Although many other marine organisms have similar green fluorescent proteins, GFP traditionally refers to the protein first isolated from the jellyfish...
(GFP) that will allow easy visualization of the products of the genetic modification. While this is a useful technique, the manipulation can destroy the function of the gene, creating secondary effects and possibly calling into question the results of the experiment. More sophisticated techniques are now in development that can track protein products without mitigating their function, such as the addition of small sequences that will serve as binding motifs to monoclonal antibodies.
- Expression studies aim to discover where and when specific proteins are produced. In these experiments, the DNA sequence before the DNA that codes for a protein, known as a gene's promoter
In genetics, a promoter is a region of DNA that facilitates the transcription of a particular gene. Promoters are typically located near the genes they regulate, on the same strand and upstream .-Overview:...
, is reintroduced into an organism with the protein coding region replaced by a reporter gene such as GFP or an enzyme that catalyzes the production of a dye. Thus the time and place where a particular protein is produced can be observed. Expression studies can be taken a step further by altering the promoter to find which pieces are crucial for the proper expression of the gene and are actually bound by transcription factor proteins; this process is known as promoter bashingPromoter bashing is a technique used in molecular biology to identify the importance of a specific promoter for the proper expression of the gene. Specific point mutations are made and the transcription of the gene is then measured. The importance of a promoter can be observed by the level of...
.
Human genetic engineering
Human genetic engineering can be used to treat genetic disease, but there is a difference between treating the disease in an individual and changing the genome that gets passed down to that person's descendants (germ-line genetic engineering).
Human genetic engineering has the potential to change human beings' appearance, adaptability, intelligence, character, and behavior. It may potentially be used in creating more dramatic changes in humans. There are many unresolved ethical issues and concerns surrounding this technology, and it remains a controversial topic.
Forms
Genetic engineering can enable the transport of genes between unrelated (
transgenesisTransgenesis is the process of introducing an exogenous gene – called a transgene – into a living organism so that the organism will exhibit a new property and transmit that property to its offspring....
) or related (
cisgenesisthumb|right|200px|Potatoes after treatment with [[Phytophthora infestans]]. The normal potatoes have blight but the cisgenic potatoes are healthyCisgenesis is the process by which genes can be artificially transferred between organisms that could be conventionally bred. Unlike in transgenesis,...
) organisms that would otherwise be unable to occur naturally, due to differences in
anatomyAnatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy and plant anatomy...
or the incorrespondence between the DNA structures. This form of genetic engineering can produce unpredictable results to the
genomeIn modern molecular biology the genome refers to all of its hereditary information encoded in DNA .The genome includes both the genes and the non-coding sequences of the DNA. The term was adapted in 1920 by Hans Winkler, Professor of Botany at the University of Hamburg, Germany...
of the organisms, and can be related to those
mutationIn biology, a mutation is a randomly derived change to the nucleotide sequence of the genetic material of an organism.Mutations can be caused by copying errors in the genetic material during cell division, or by exposure to mutagens , or can be induced by the organism itself, by cellular processes...
processes.
Advantages and disadvantages
The modification of the
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information...
structures of agricultural crops can increase the growth rates and even resistance to different diseases caused by
pathogenA pathogen , infectious agent, or germ, is a biological agent that causes disease or illness to its host....
s and parasites. This is extremely beneficial as it can greatly increase the production of food sources with the usage of fewer resources that would be required to host the world's growing populations. These modified crops would also reduce the usage of chemicals, such as
fertilizerFertilizers are chemical compounds applied to promote plant and fruit growth. Fertilizers are usually applied either through the soil or by foliar feeding...
s and
pesticideA pesticide is a substance or mixture of substances used to kill a pest.A pesticide is any substance or mixture of substance intended for:- preventing, destroying, repelling or mitigating any pest....
s, and therefore decrease the severity and frequency of the damages produced by these chemical
pollutionPollution is the introduction of contaminants into an environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms . Pollution can take the form of chemical substances, or energy, such as noise, heat, or light...
. Domesticated animals can undergo the same mechanism. Genetic engineering can also increase the genetic diversity of species populations, especially those that are classified as being endangered. Increase in genetic diversity would enabled these organisms to evolve more efficiently that would allow better adaptation to the ecosystems they inhabit. It would also reduce the vulnerability of certain diseases produced by pathogens, as well as decrease the risk of
inbreedingInbreeding is breeding between close relatives, whether plant or animal. If practiced repeatedly, it can lead to exposure of recessive, deleterious traits. This generally leads to a decreased fitness of a population, which is called inbreeding depression. Deleterious alleles causing inbreeding...
that would produce infertile youths. Genetic engineering can be performed to increase to the efficiency of the ecosystem services provided by the other organisms. For example, the modification of a tree's genes could perhaps increase the root systems of these organisms reduce the damage produced by flood phenomena through
flood mitigationFlood mitigation involves managing the effects of flooding, rather than trying to prevent it altogether. It is management of people, through measures such as evactuation and properties dry/wet proofing for example....
.
Opposition and criticism
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