GMO Genetic modification

Genetic engineering, also called genetic modification or genetic manipulation, is the modification and manipulation of an organism's genes using technology. It is a set of technologies used to change the genetic makeup of cells, including the transfer of genes within and across species boundaries to produce improved or novel organisms.

New DNA is obtained by either isolating and copying the genetic material of interest using recombinant DNA methods or by artificially synthesising the DNA. A construct is usually created and used to insert this DNA into the host organism. The first recombinant DNA molecule was made by Paul Berg in 1972 by combining DNA from the monkey virus SV40 with the lambda virus. As well as inserting genes, the process can be used to remove, or "knock out", genes. The new DNA can be inserted randomly, or targeted to a specific part of the genome.^[1]

An organism that is generated through genetic engineering is considered to be genetically modified (GM) and the resulting entity is a genetically modified organism (GMO). The first GMO was a bacterium generated by Herbert Boyer and Stanley Cohen in 1973. Rudolf Jaenisch created the first GM animal when he inserted foreign DNA into a mouse in 1974. The first company to focus on genetic engineering, Genentech, was founded in 1976 and started the production of human proteins.

Genetically engineered human insulin was produced in 1978 and insulin-producing bacteria were commercialised in 1982. Genetically modified food has been sold since 1994, with the release of the Flavr Savr tomato. The Flavr Savr was engineered to have a longer shelf life, but most current GM crops are modified to increase resistance to insects and herbicides. GloFish, the first GMO designed as a pet, was sold in the United States in December 2003. In 2016 salmon modified with a growth hormone were sold.

Genetic engineering has been applied in numerous fields including research, medicine, industrial biotechnology and agriculture. In research, GMOs are used to study gene function and expression through loss of function, gain of function, tracking and expression experiments. By knocking out genes responsible for certain conditions it is possible to create animal model organisms of human diseases. As well as producing hormones, vaccines and other drugs, genetic engineering has the potential to cure genetic diseases through gene therapy. The same techniques that are used to produce drugs can also have industrial applications such as producing enzymes for laundry detergent, cheeses and other products.

The rise of commercialised genetically modified crops has provided economic benefit to farmers in many different countries, but has also been the source of most of the controversy surrounding the technology. This has been present since its early use; the first field trials were destroyed by anti-GM activists.

Although there is a scientific consensus that currently available food derived from GM crops poses no greater risk to human health than conventional food, critics consider GM food safety a leading concern. Gene flow, impact on non-target organisms, control of the food supply and intellectual property rights have also been raised as potential issues. These concerns have led to the development of a regulatory framework, which started in 1975. It has led to an international treaty, the Cartagena Protocol on Biosafety, that was adopted in 2000. Individual countries have developed their own regulatory systems regarding GMOs, with the most marked differences occurring between the US and Europe.

IUPAC definition

Genetic engineering: Process of inserting new genetic information into existing cells in order to modify a specific organism for the purpose of changing its characteristics.

Overview

Comparison of conventional plant breeding with transgenic and cisgenic genetic modification

Genetic engineering is a process that alters the genetic structure of an organism by either removing or introducing DNA, or modifying existing genetic material in situ. Unlike traditional animal and plant breeding, which involves doing multiple crosses and then selecting for the organism with the desired phenotype, genetic engineering takes the gene directly from one organism and delivers it to the other. This is much faster, can be used to insert any genes from any organism (even ones from different domains) and prevents other undesirable genes from also being added.^[4]

Genetic engineering could potentially fix severe genetic disorders in humans by replacing the defective gene with a functioning one.^[5] It is an important tool in research that allows the function of specific genes to be studied.^[6] Drugs, vaccines and other products have been harvested from organisms engineered to produce them.^[7] Crops have been developed that aid food security by increasing yield, nutritional value and tolerance to environmental stresses.^[8]

The DNA can be introduced directly into the host organism or into a cell that is then fused or hybridised with the host.^[9] This relies on recombinant nucleic acid techniques to form new combinations of heritable genetic material followed by the incorporation of that material either indirectly through a vector system or directly through micro-injection, macro-injection or micro-encapsulation.

Genetic engineering does not normally include traditional breeding, in vitro fertilisation, induction of polyploidy, mutagenesis and cell fusion techniques that do not use recombinant nucleic acids or a genetically modified organism in the process.^[9] However, some broad definitions of genetic engineering include selective breeding.^[10] Cloning and stem cell research, although not considered genetic engineering,^[11] are closely related and genetic engineering can be used within them.^[12] Synthetic biology is an emerging discipline that takes genetic engineering a step further by introducing artificially synthesised material into an organism.^[13]

Plants, animals or microorganisms that have been changed through genetic engineering are termed genetically modified organisms or GMOs.^[14] If genetic material from another species is added to the host, the resulting organism is called transgenic. If genetic material from the same species or a species that can naturally breed with the host is used the resulting organism is called cisgenic.^[15] If genetic engineering is used to remove genetic material from the target organism the resulting organism is termed a knockout organism.^[16] In Europe genetic modification is synonymous with genetic engineering while within the United States of America and Canada genetic modification can also be used to refer to more conventional breeding methods.^[17][18][19]

History

Main article: History of genetic engineering

Humans have altered the genomes of species for thousands of years through selective breeding, or artificial selection^{[20]: 1 [21]: 1} as contrasted with natural selection. More recently, mutation breeding has used exposure to chemicals or radiation to produce a high frequency of random mutations, for selective breeding purposes. Genetic engineering as the direct manipulation of DNA by humans outside breeding and mutations has only existed since the 1970s.

The term "genetic engineering" was first coined by the Russian-born geneticist Nikolay Timofeev-Ressovsky in his 1934 paper "The Experimental Production of Mutations", published in the British journal Biological Reviews.^[22] Jack Williamson used the term in his science fiction novel Dragon's Island, published in 1951^[23] – one year before DNA's role in heredity was confirmed by Alfred Hershey and Martha Chase,^[24] and two years before James Watson and Francis Crick showed that the DNA molecule has a double-helix structure – though the general concept of direct genetic manipulation was explored in rudimentary form in Stanley G. Weinbaum's 1936 science fiction story Proteus Island.^[25][26]

In 1974 Rudolf Jaenisch created a genetically modified mouse, the first GM animal.

In 1972, Paul Berg created the first recombinant DNA molecules by combining DNA from the monkey virus SV40 with that of the lambda virus.^[27] In 1973 Herbert Boyer and Stanley Cohen created the first transgenic organism by inserting antibiotic resistance genes into the plasmid of an Escherichia coli bacterium.^[28][29]

A year later Rudolf Jaenisch created a transgenic mouse by introducing foreign DNA into its embryo, making it the world's first transgenic animal^[30] These achievements led to concerns in the scientific community about potential risks from genetic engineering, which were first discussed in depth at the Asilomar Conference in 1975. One of the main recommendations from this meeting was that government oversight of recombinant DNA research should be established until the technology was deemed safe.^[31][32]

In 1976 Genentech, the first genetic engineering company, was founded by Herbert Boyer and Robert Swanson and a year later the company produced a human protein (somatostatin) in E. coli. Genentech announced the production of genetically engineered human insulin in 1978.^[33] In 1980, the U.S. Supreme Court in the Diamond v. Chakrabarty case ruled that genetically altered life could be patented.^[34] The insulin produced by bacteria was approved for release by the Food and Drug Administration (FDA) in 1982.^[35]

In 1983, a biotech company, Advanced Genetic Sciences (AGS) applied for U.S. government authorisation to perform field tests with the ice-minus strain of Pseudomonas syringae to protect crops from frost, but environmental groups and protestors delayed the field tests for four years with legal challenges.^[36] In 1987, the ice-minus strain of P. syringae became the first genetically modified organism (GMO) to be released into the environment^[37] when a strawberry field and a potato field in California were sprayed with it.^[38] Both test fields were attacked by activist groups the night before the tests occurred: "The world's first trial site attracted the world's first field trasher".^[37]

The first field trials of genetically engineered plants occurred in France and the US in 1986, tobacco plants were engineered to be resistant to herbicides.^[39] The People's Republic of China was the first country to commercialise transgenic plants, introducing a virus-resistant tobacco in 1992.^[40] In 1994 Calgene attained approval to commercially release the first genetically modified food, the Flavr Savr, a tomato engineered to have a longer shelf life.^[41]

In 1994, the European Union approved tobacco engineered to be resistant to the herbicide bromoxynil, making it the first genetically engineered crop commercialised in Europe.^[42] In 1995, Bt potato was approved safe by the Environmental Protection Agency, after having been approved by the FDA, making it the first pesticide producing crop to be approved in the US.^[43] In 2009 11 transgenic crops were grown commercially in 25 countries, the largest of which by area grown were the US, Brazil, Argentina, India, Canada, China, Paraguay and South Africa.^[44]

In 2010, scientists at the J. Craig Venter Institute created the first synthetic genome and inserted it into an empty bacterial cell. The resulting bacterium, named Mycoplasma laboratorium, could replicate and produce proteins.^[45][46] Four years later this was taken a step further when a bacterium was developed that replicated a plasmid containing a unique base pair, creating the first organism engineered to use an expanded genetic alphabet.^[47][48] In 2012, Jennifer Doudna and Emmanuelle Charpentier collaborated to develop the CRISPR/Cas9 system,^[49][50] a technique which can be used to easily and specifically alter the genome of almost any organism.^[51]

Process

Main article: Genetic engineering techniques

Polymerase chain reaction is a powerful tool used in molecular cloning.

Creating a GMO is a multi-step process. Genetic engineers must first choose what gene they wish to insert into the organism. This is driven by what the aim is for the resultant organism and is built on earlier research. Genetic screens can be carried out to determine potential genes and further tests then used to identify the best candidates. The development of microarrays, transcriptomics and genome sequencing has made it much easier to find suitable genes.^[52] Luck also plays its part; the Roundup Ready gene was discovered after scientists noticed a bacterium thriving in the presence of the herbicide.^[53]

Gene isolation and cloning

Main article: Molecular cloning

The next step is to isolate the candidate gene. The cell containing the gene is opened and the DNA is purified.^[54] The gene is separated by using restriction enzymes to cut the DNA into fragments^[55] or polymerase chain reaction (PCR) to amplify up the gene segment.^[56] These segments can then be extracted through gel electrophoresis. If the chosen gene or the donor organism's genome has been well studied it may already be accessible from a genetic library.

If the DNA sequence is known, but no copies of the gene are available, it can also be artificially synthesised.^[57] Once isolated the gene is ligated into a plasmid that is then inserted into a bacterium. The plasmid is replicated when the bacteria divide, ensuring unlimited copies of the gene are available.^[58] The RK2 plasmid is notable for its ability to replicate in a wide variety of single-celled organisms, which makes it suitable as a genetic engineering tool.^[59]

Before the gene is inserted into the target organism it must be combined with other genetic elements. These include a promoter and terminator region, which initiate and end transcription. A selectable marker gene is added, which in most cases confers antibiotic resistance, so researchers can easily determine which cells have been successfully transformed. The gene can also be modified at this stage for better expression or effectiveness. These manipulations are carried out using recombinant DNA techniques, such as restriction digests, ligations and molecular cloning.^[60]

Inserting DNA into the host genome

Main article: Gene delivery...

Controversy

Main article: Genetically modified food controversies

Critics have objected to the use of genetic engineering on several grounds, including ethical, ecological and economic concerns. Many of these concerns involve GM crops and whether food produced from them is safe and what impact growing them will have on the environment. These controversies have led to litigation, international trade disputes, and protests, and to restrictive regulation of commercial products in some countries.^[179]

Accusations that scientists are "playing God" and other religious issues have been ascribed to the technology from the beginning.^[180] Other ethical issues raised include the patenting of life,^[181] the use of intellectual property rights,^[182] the level of labeling on products,^[183][184] control of the food supply^[185] and the objectivity of the regulatory process.^[186] Although doubts have been raised,^[187] economically most studies have found growing GM crops to be beneficial to farmers.^{[188][189][190]}

Gene flow between GM crops and compatible plants, along with increased use of selective herbicides, can increase the risk of "superweeds" developing.^[191] Other environmental concerns involve potential impacts on non-target organisms, including soil microbes,^[192] and an increase in secondary and resistant insect pests.^[193][194] Many of the environmental impacts regarding GM crops may take many years to be understood and are also evident in conventional agriculture practices.^[192][195] With the commercialisation of genetically modified fish there are concerns over what the environmental consequences will be if they escape.^[196]

There are three main concerns over the safety of genetically modified food: whether they may provoke an allergic reaction; whether the genes could transfer from the food into human cells; and whether the genes not approved for human consumption could outcross to other crops.^[197] There is a scientific consensus^{[198][199][200][201]} that currently available food derived from GM crops poses no greater risk to human health than conventional food,^{[202][203][204][205][206]} but that each GM food needs to be tested on a case-by-case basis before introduction.^{[207][208][209]} Nonetheless, members of the public are less likely than scientists to perceive GM foods as safe.^{[210][211][212][213]}

The climate crisis may well drive introduction of GMO crops better able to withstand drought, flood, freezing and saltwater.

In popular culture

Main article: Genetics in fiction § Genetic engineering

Genetic engineering features in many science fiction stories.^[214] Frank Herbert's novel The White Plague describes the deliberate use of genetic engineering to create a pathogen which specifically kills women.^[214] Another of Herbert's creations, the Dune series of novels, uses genetic engineering to create the powerful Tleilaxu.^[215]

Few films have informed audiences about genetic engineering, with the exception of the 1978 The Boys from Brazil and the 1993 Jurassic Park, both of which make use of a lesson, a demonstration, and a clip of scientific film.^[216][217] Genetic engineering methods are weakly represented in film; Michael Clark, writing for the Wellcome Trust, calls the portrayal of genetic engineering and biotechnology "seriously distorted"^[217] in films such as The 6th Day. In Clark's view, the biotechnology is typically "given fantastic but visually arresting forms" while the science is either relegated to the background or fictionalised to suit a young audience.^[217]

In the 2007 video game, BioShock, genetic engineering plays an important role in the central storyline and universe. The game takes place in the fictional underwater dystopia Rapture, in which its inhabitants possess genetic superhuman abilities after injecting themselves with "plasmids", a serum which grants such powers. Also in the city of Rapture are "Little Sisters", little girls who are generically engineered, as well as a side-plot in which a cabaret singer sells her foetus to genetic scientists who implant false memories into the newborn and genetically engineer it to grow into an adult.