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8.8: Transgenic organisms - Biology


General principles of transgenesis

Transgenic organisms contain foreign DNA that has been introduced using biotechnology. Foreign DNA (the transgene) is defined here as DNA from another species, or else recombinant DNA from the same species that has been manipulated in the laboratory then reintroduced. The terms transgenic organism and genetically modified organism (GMO) are generally synonymous. The process of creating transgenic organisms or cells to be come whole organisms with a permanent change to their germline has been called either transformation or transfection. (Unfortunately, both words have alternate meanings. Transformation also refers to the process of mammalian cell becoming cancerous, while transfection also refers to the process of introducing DNA into cells in culture, either bacterial or eukaryote, for a temporary use, not germ line changes.) Transgenic organisms are important research tools, and are often used when exploring a gene’s function. Transgenesis is also related to the medical practice of gene therapy, in which DNA is transferred into a patient’s cells to treat disease. Transgenic organisms are widespread in agriculture. Approximately 90% of canola, cotton, corn, soybean, and sugar beets grown in North America are transgenic. No other transgenic livestock or crops (except some squash, papaya, and alfalfa) are currently produced in North America.

To make a transgenic cell, DNA must first be transferred across the cell membrane, (and, if present, across the cell wall), without destroying the cell. In some cases, naked DNA (meaning plasmid or linear DNA that is not bound to any type of carrier) may be transferred into the cell by adding DNA to the medium and temporarily increasing the porosity of the membrane, for example by electroporation. When working with larger cells, naked DNA can also be microinjected into a cell using a specialized needle. Other methods use vectors to transport DNA across the membrane. Note that the word “vector” as used here refers to any type of carrier, and not just plasmid vectors. Vectors for transformation/transfection include vesicles made of lipids or other polymers that surround DNA; various types of particles that carry DNA on their surface; and infectious viruses and bacteria that naturally transfer their own DNA into a host cell, but which have been engineered to transfer any DNA molecule of interest. Usually the foreign DNA is a complete expression unit that includes its own cis-regulators (e.g. promoter) as well as the gene that is to be transcribed.

When the objective of an experiment is to produce a stable (i.e. heritable) transgenic eukaryote, the foreign DNA must be incorporated into the host’s chromosomes. For this to occur, the foreign DNA must enter the host’s nucleus, and recombine with one of the host’s chromatids. In some species, the foreign DNA is inserted at a random location in a chromatid, probably wherever strand breakage and non-homologous end joining happen to occur. In other species, the foreign DNA can be targeted to a particular locus, by flanking the foreign DNA with DNA that is homologous to the host’s DNA at that locus. The foreign DNA is then incorporated into the host’s chromosomes through homologous recombination.

Furthermore, to produce multicellular organisms in which all cells are transgenic and the transgene is stably inherited, the cell that was originally transformed must be either a gamete or must develop into tissues that produce gametes. Transgenic gametes can eventually be mated to produce homozygous, transgenic offspring. The presence of the transgene in the offspring is typically confirmed using PCR or Southern blotting, and the expression of the transgene can be measured using reverse-transcription PCR (RT-PCR), RNA blotting, and Western (protein blotting).

The rate of transcription of a transgene is highly dependent on the state of the chromatin into which it is inserted (i.e. position effects), as well as other factors. Therefore, researchers often generate several independently transformed/transfected lines with the same transgene, and then screen for the lines with the highest expression. It is also good practice to clone and sequence the transgenic locus from a newly generated transgenic organism, since errors (truncations, rearrangements, and other mutations) can be introduced during transformation/transfection.

Producing a transgenic plant

The most common method for producing transgenic plants is Agrobacterium-mediated transformation (Figure (PageIndex{1})). Agrobacterium tumifaciens is a soil bacterium that, as part of its natural pathogenesis, injects its own tumor-inducing (Ti) plasmid into cells of a host plant. The natural Ti plasmid encodes growth-promoting genes that cause a gall (i.e. tumor) to form on the plant, which also provides an environment for the pathogen to proliferate. Molecular biologists have engineered the Ti plasmid by removing the tumor-inducing genes and adding restriction sites that make it convenient to insert any DNA of interest. This engineered version is called a T-DNA (transfer-DNA) plasmid; the bacterium transfers a linear fragment of this plasmid that includes the conserved “left-border (LB)”, and right-border (RB)” DNA sequences, and anything in between them (up to about 10 kb). The linear T-DNA fragment is transported into the nucleus, where it recombines with the host-DNA, probably wherever random breakages occur in the host’s chromosomes.

In Arabidopsis and a few other species, flowers can simply be dipped in a suspension of Agrobacterium, and ~1% of the resulting seeds will be transformed. In most other plant species, cells are induced by hormones to form a mass of undifferentiated tissues called a callus. The Agrobacterium is applied to a callus and a few cells are transformed, which can then be induced by other hormones to regenerate whole plants (Figure (PageIndex{2})). Some plant species are resistant (i.e. “recalcitrant”) to transformation by Agrobacterium. In these situations, other techniques must be used such as particle bombardment, whereby DNA is non-covalently attached to small metallic particles, which are accelerated by compressed air into callus tissue, from which complete transgenic plants can sometimes be regenerated. In all transformation methods, the presence of a selectable marker (e.g. a gene that confers antibiotic resistance or herbicide resistance) is useful for distinguishing transgenic cells from non-transgenic cells at an early stage of the transformation process.

Producing a transgenic mouse

In a commonly used method for producing a transgenic mouse, stem cells are removed from a mouse embryo, and a transgenic DNA construct is transferred into the stem cells using electroporation, and some of this transgenic DNA enters the nucleus, where it may undergo homologous recombination (Figure (PageIndex{3})). The transgenic DNA construct contains DNA homologous to either side of a locus that is to be targeted for replacement. If the objective of the experiment is simply to delete (“knock-out”) the targeted locus, the host’s DNA can simply be replaced by selectable marker, as shown. It is also possible to replace the host’s DNA at this locus with a different version of the same gene, or a completely different gene, depending on how the transgenic construct is made. Cells that have been transfected and express the selectable marker (i.e. resistance to the antibiotic neomycin resistance, neoR, in this example) are distinguished from unsuccessfully transfected cells by their ability to survive in the presence of the selective agent (e.g. an antibiotic). Transfected cells are then injected into early stage embryos, and then are transferred to a foster mother. The resulting pups are chimeras, meaning that only some of their cells are transgenic. Some of the chimeras will produce gametes that are transgenic, which when mated with a wild-type gamete, will produce mice that are hemizygous for the transgene. Unlike the chimeras, these hemizygotes carry the transgene in all of their cells. Through further breeding, mice that are homozygous for the transgene can be obtained.

Human gene therapy

Many different strategies for human gene therapy are under development. In theory, either the germline or somatic cells may be targeted for transfection, but most research has focused on somatic cell transfection, because of risks and ethical issues associated with germline transformation. Gene therapy approaches may be further classified as either ex vivo or in vivo, with the former meaning that cells (e.g. stem cells) are transfected in isolation before being introduced to the body, where they replace defective cells. Ex vivo gene therapies for several blood disorders (e.g. immunodeficiencies, thalassemias) are undergoing clinical trials. For in vivo therapies, the transfection occurs within the patient. The objective may be either stable integration, or non-integrative transfection. As described above, stable transfection involves integration into the host genome. In the clinical context, stable integration may not be necessary, and carries with it higher risk of inducing mutations in either the transgene or host genome). In contrast, transient transfection does not involve integration into the host genome and the transgene may therefore be delivered to the cell as either RNA or DNA. Advantages of RNA delivery include that no promoter is needed to drive expression of the transgene. Besides mRNA transgenes, which could provide a functional version of a mutant protein, there is great interest in delivery of siRNA (small-inhibitory RNAs), which can be used to silence specific genes in the host cell’s genome.

Vectors for in vivo gene therapy must be capable of delivering DNA or RNA to a large proportion of the targeted cells, without inducing a significant immune response, or having any toxic effects. Ideally, the vectors should also have high specificity for the targeted cell type. Vectors based on viruses (e.g. lentiviruses) are being developed for in both in vivo and ex vivo gene therapies. Other, non-viral vectors (e.g. vesicles and nanoparticles) are also being developed for gene therapy as well.


What Are Transgenic Animals?

Transgenic animals are animals that have been cloned. The medical and biotechnological uses of animal cloning are almost innumerable, as many diseases have been eradicated thanks to the production of these transgenic animals. Due to the controversial concept of cloning and scientific testing on animals, there are many questions that revolve around this topic. The most commonly asked question remains: what are the uses, advantages and disadvantages of transgenic animals?

In this AnimalWised article, we will be explaining what transgenic animal are and what the production of cloning animals includes. Additionally, we will be presenting you with some examples of transgenic animals.


The History of Transgenesis

A transgenic mouse carries within its genome an artificial DNA construct (transgene) that is deliberately introduced by an experimentalist. These animals are widely used to understand gene function and protein function. When addressing the history of transgenic mouse technology, it is apparent that a number of basic science research areas laid the groundwork for success. These include reproductive science, genetics and molecular biology, and micromanipulation and microscopy equipment. From reproductive physiology came applications on how to optimize mouse breeding, how to superovulate mice to produce zygotes for DNA microinjection or preimplantation embryos for combination with embryonic stem (ES) cells, and how to return zygotes and embryos to a pseudopregnant surrogate dam for gestation and birth. From developmental biology, it was learned how to micromanipulate embryos for morula aggregation and blastocyst microinjection and how to establish germline competent ES cells. From genetics came the foundational principles governing the inheritance of genes, the interactions of gene products, and an understanding of the phenotypic consequences of genetic mutations. From molecular biology came a panoply of tools and reagents that are used to clone DNA transgenes, to detect the presence of transgenes, to assess gene expression by measuring transcription, and to detect proteins in cells and tissues. Technical advances in light microscopes, micromanipulators, micropipette pullers, and ancillary equipment made it possible for experimentalists to insert thin glass needles into zygotes or embryos under controlled conditions to inject DNA solutions or ES cells. To fully discuss the breadth of contributions of these numerous scientific disciplines to a comprehensive history of transgenic science is beyond the scope of this work. Examples will be used to illustrate scientific developments central to the foundation of transgenic technology and that are in use today.

Keywords: Micromanipulation Superovulation Transgene Transgenesis Transgenic core facility Transgenic mice.


Transgenic Organisms

Image courtesy of the National Human Genome Research Institute

Modern genetic technology can be used to modify the genomes of living organisms. This process is also known as “genetic engineering.” Genes of one species can be modified, or genes can be transplanted from one species to another. Genetic engineering is made possible by recombinant DNA technology. Organisms that have altered genomes are known as transgenic. Most transgenic organisms are generated in the laboratory for research purposes. For example, “knock-out” mice are transgenic mice that have a particular gene of interest disabled. By studying the effects of the missing gene, researchers can better understand the normal function of the gene.

Transgenic organisms have also been developed for commercial purposes. Perhaps the most famous examples are food crops like soy and corn that have been genetically modified for pest and herbicide resistance. These crops are widely known as “GMOs” (genetically modified organisms). Here are few other examples of transgenic organisms with commercial value:

* Golden rice: modified rice that produces beta-carotene, the precursor to vitamin A. Vitamin A deficiency is a public health problem for millions of people around the world,
particularly in Africa and Southeast Asia. Golden rice is still waiting regulatory approval.

* Goats that produce important proteins in their milk: goats modified to produce FDA-
approved human antithrombin (ATryn), which is used to treat a rare blood clotting
disorder in humans. Goats have also been genetically modified to produce spider silk,
one of the strongest materials known to man, in their milk. Proposed uses for this
recombinant spider silk range from artificial tendons to bulletproof vests.

* Vaccine producing bananas: genetically engineered bananas that contain a vaccine. Bananas provide an easy means for delivering a vaccine (especially to children) without the need for a medical professional that is trained in giving shots. Edible vaccines are still in development.

*Chymosin producing microorganisms: yeast, fungi, or bacteria modified to produce the enzyme
chymosin, which splits milk to make cheese. Traditionally, rennet (found in cow stomachs) is used to clot cheese. But, when the demand for firm cheeses surpassed the amount of rennet available, recombinant chymosin was developed and is used widely today.

* Low acrylamide potatoes: The J.R. Simplot Company has developed a strain of transgenic potatoes that are modified to resist bruising and browning when cut. They also produce less of the amino acid asparagine. Asparagine contributes to the formation of acrylamide, a known neurotoxin and likely carcinogen, when potatoes are cooked at high temperatures. This means healthier french fries!

CLICK HERE to learn more about recombinant DNA technology


Recombinant DNA

The phenomenon to construct transgenic organisms is recombinant DNA. The recombination is observable during meiosis, as homologous chromosomes form pairs and physically exchange pieces of their DNA with one another. DNA recombination is a complex process here, both the strands of the two DNA molecules get broken and rejoined. As they are swapped, new molecules are rejoined, such that the original molecules are restored. Recombination depends on the nature of the starting molecules. The linear DNA molecule, for example, chromosome and the circular DNA molecule, are used in the process, as the linear molecule integrates into a plasmid.

Homologous recombination is the most frequent form of naturally occurring recombination, whereas non-homologous recombination is used in the formation of transgenic organisms. Non-homologous recombination lacks DNA homology between the chromosome and the novel DNA. The specialized form of homologous recombination is site-specific recombination. The site-specific recombination is similar to the homologous recombination, but the homology's length is very short.


A Transgenic Organism Is: : Genetic Engineering Notes Biology Mrs Mccomas

A Transgenic Organism Is: : Genetic Engineering Notes Biology Mrs Mccomas. Transgenic organisms are organisms whose genetic makeup has been altered by the addition of genetic material from an unrelated organism. In this way transgenic organisms might be thought. Trans = genic = organism = transgenic organisms are: Genetically modified organisms (gmos) are produced by inserting genetic material (sometimes from another species) into a plant such that the new genetic material will provide the plant the ability to exhibit some desirable trait (i.e., genetic engineering). Bacterial transformation is another example of a process that leads to a transgenic organism. There are many ways you can genetically modify something. Genetically modified organism (gmo) specializes in providing 129sv/ev and c57bl/6 mouse gene knockout/knockin services. A transgenic organism is an organism which has been modified with genetic material from another species. Transgenic modification is one type of genetic modification. This image (to the right) (courtesy of r.

A transgenic organism is a viable organism whose genome is engineered to contain a certain amount of foreign dna transgenic organism is a modern genetic technology. Already today thousands of products come from. • the organism carrying it (the transgene) is referred to as a transgenic organism. The transgene may either be a different version of one of the organism's genes or a gene that does not exist in their genome. Generally, two different organisms become sexually compatible only if they belong to the same species.

Https Digital Wpi Edu Downloads 5425kb17h from Until recently, the fear that a transgenic organism might escape and infiltrate a natural ecosystem was based on theoretical scenarios. T… a section of mouse dna is joined to a b… when a bacterial plasmid transfers a pi… check for carriers of a trait. The process of creating transgenic. The introduction of a transgene, in a process known as transgenesis, has the potential to change the phenotype of an organism. These crops are widely known as gmos (genetically modified organisms). This foreign material can come from transgenic animals or plants are those that have genes from other organisms added to their dna. Generally, two different organisms become sexually compatible only if they belong to the same species. For instance, a plant may be given genetic material that increases its resistance to frost. Other articles where transgenic organism is discussed:

Transgenic organisms are organisms whose genetic material has been changed by the addition of foreign genes.

Transgenic organism is an organism whose genome has been genetically modified by introduction of novel dna. A transgenic animal, for instance, would be an animal that underwent genetic engineering. Transgenic organism synonyms, transgenic organism pronunciation, transgenic organism translation, english dictionary definition of transgenic organism. Transgenic organisms have also been developed for commercial purposes. Transgenic organisms are organisms whose genetic material has been changed by the addition of foreign genes. Let's break apart the word: In this way transgenic organisms might be thought. A transgene is a gene that has been transferred naturally, or by any of a number of genetic engineering techniques from one organism to another. Through the alterations of these genes, techniques in the study of genetics are generally known as recombinant dna technology. A transgenic organism is a type of genetically modified organism (gmo) that has genetic material from another species that provides a useful trait. Generally, two different organisms become sexually compatible only if they belong to the same species. An organism that contains one or more artificially inserted genes, typically from another species. A transgenic organism is one whose genome has been subject to artificial modification.

The transgenic organism is an organism that has altered genes either by the insertion of one or several foreign genes originating from the same species or the genus or by the deletion or inactivation of the selected genes (knockout organisms). T… a section of mouse dna is joined to a b… when a bacterial plasmid transfers a pi… check for carriers of a trait. A transgenic organism is an organism which has been modified with genetic material from another species. The use of the chemical compound colchicine. Generally, two different organisms become sexually compatible only if they belong to the same species. You can do gene silencing, which in many cases the transgene has landed any old place and the resulting organism works. Transgenic organism is an organism whose genome has been genetically modified by introduction of novel dna.

Transgenic Organisms A Transgenic Organism Is One Into from slidetodoc.com Transgenic organisms are genetically engineered to carry transgenes—genes from a different species—as part of their genome. Gmo an organism whose genetic characteristics have been altered by the insertion of a modified gene or a gene from another. In this way transgenic organisms might be thought. Let's break apart the word: Foreign dna (the transgene ) is defined here as dna from another the terms transgenic organism and genetically modified organism (gmo) are generally synonymous. The transgenic organism is an organism that has altered genes either by the insertion of one or several foreign genes originating from the same species or the genus or by the deletion or inactivation of the selected genes (knockout organisms). This foreign material can come from transgenic animals or plants are those that have genes from other organisms added to their dna. Perhaps the most famous examples are food crops like soy and corn that have been genetically modified for pest and herbicide resistance. Transgenic modification is one type of genetic modification.

Foreign dna (the transgene ) is defined here as dna from another the terms transgenic organism and genetically modified organism (gmo) are generally synonymous.

A transgenic organism is an organism which has been modified with genetic material from another species. A transgenic animal, for instance, would be an animal that underwent genetic engineering. The transgenic organism is an organism that has altered genes either by the insertion of one or several foreign genes originating from the same species or the genus or by the deletion or inactivation of the selected genes (knockout organisms). A transgenic organism is a type of genetically modified organism (gmo) that has genetic material from another species that provides a useful trait. Explain why the transgenes in genetically modified food are safe for human consumption. A transgenic organism is an organism that contains a. Transgenic organism's outstanding troubleshooters can. Genetically modified organism (gmo) specializes in providing 129sv/ev and c57bl/6 mouse gene knockout/knockin services. Gmo an organism whose genetic characteristics have been altered by the insertion of a modified gene or a gene from another. A transgenic organism is a viable organism whose genome is engineered to contain a certain amount of foreign dna transgenic organism is a modern genetic technology. For instance, a plant may be given genetic material that increases its resistance to frost. Transgenic modification is one type of genetic modification.

Transgenic organisms contain foreign dna that has been introduced using biotechnology. …an organism's genes) transgenic plant cells can be made into plants by growing the cells on special hormones. But here, if the recipient organism is a plant, the. The transgene may either be a different version of one of the organism's genes or a gene that does not exist in their genome. A transgene is a gene that has been transferred naturally, or by any of a number of genetic engineering techniques from one organism to another. Genetically modified organisms (gmos) are produced by inserting genetic material (sometimes from another species) into a plant such that the new genetic material will provide the plant the ability to exhibit some desirable trait (i.e., genetic engineering). Trans = genic = organism = transgenic organisms are: This image (to the right) (courtesy of r.

Transgenic Organismspp from image.slidesharecdn.com But here, if the recipient organism is a plant, the. Transgenic organisms have also been developed for commercial purposes. A transgenic organism may result when foreign dna is inserted into the nucleus of a fertilized embryo. This may involve artificial selection (controlled species crossing ) or gene insertion techniques in the. Genetically modified organisms (gmos) are produced by inserting genetic material (sometimes from another species) into a plant such that the new genetic material will provide the plant the ability to exhibit some desirable trait (i.e., genetic engineering). In this way transgenic organisms might be thought. The use of the chemical compound colchicine. The transgenic organism is an organism that has altered genes either by the insertion of one or several foreign genes originating from the same species or the genus or by the deletion or inactivation of the selected genes (knockout organisms).

Until recently, the fear that a transgenic organism might escape and infiltrate a natural ecosystem was based on theoretical scenarios.

Transgenic organism's outstanding troubleshooters can. You can do gene silencing, which in many cases the transgene has landed any old place and the resulting organism works. The genetic modification is accomplished by inserting dna into an embryo with the assistance of a virus, a plasmid, or a gene gun. Transgenesis provides the potential for an organism to express a trait that it normally would not. A transgenic organism may result when foreign dna is inserted into the nucleus of a fertilized embryo. It is an organism that has had genes inserted (or moved into) from a different organism slideshow 2661807 by astrid. Genetically modified organism (gmo) and transgenic organism are two terms we use interchangeably. The use of the chemical compound colchicine. Genetically modified organism (gmo) specializes in providing 129sv/ev and c57bl/6 mouse gene knockout/knockin services. Foreign dna (the transgene ) is defined here as dna from another the terms transgenic organism and genetically modified organism (gmo) are generally synonymous. But here, if the recipient organism is a plant, the.

The embryo is allowed to develop, and the mature organism will.

Transgenic organisms contain foreign dna that has been introduced using biotechnology.

Transgenic is the term used to describe the genetically modified organisms with the use of foreign genes from sexually incompatible organisms.

The transgene may either be a different version of one of the organism's genes or a gene that does not exist in their genome.

• the organism carrying it (the transgene) is referred to as a transgenic organism.

A transgenic organism is one whose genome has been subject to artificial modification.

A transgenic organism is an organism which has been modified with genetic material from another species.

Transgenic organisms have also been developed for commercial purposes.

What is the purpose of a test cross?

Genetically modified organisms (gmos) are produced by inserting genetic material (sometimes from another species) into a plant such that the new genetic material will provide the plant the ability to exhibit some desirable trait (i.e., genetic engineering).

Transgenic organisms have also been developed for commercial purposes.

The transgenic organism is an organism that has altered genes either by the insertion of one or several foreign genes originating from the same species or the genus or by the deletion or inactivation of the selected genes (knockout organisms).

Transgenic organism's outstanding troubleshooters can.

The most famous example are food crops like soy and corn that have been.

Already today thousands of products come from.

Explain why the transgenes in genetically modified food are safe for human consumption.

Transgenic modification is one type of genetic modification.

Perhaps the most famous examples are food crops like soy and corn that have been genetically modified for pest and herbicide resistance.

Two closely related cattle are mated.

A transgenic organism is one that contains a gene or genes which have been artificially inserted instead of the organism acquiring them through reproduction.

A transgenic organism may result when foreign dna is inserted into the nucleus of a fertilized embryo.

Transgenic organism is an organism whose genome has been genetically modified by introduction of novel dna.

These crops are widely known as gmos (genetically modified organisms).

The process of creating transgenic.

A transgenic organism is one whose genome has been subject to artificial modification.


Top 5 Benefits of Transgenic Animals | Biotechnology

The following points highlight the top five benefits of transgenic animals. The benefits are: 1. Normal Physiology and Development 2. Study of Disease 3. Biological Products 4. Vaccine Safety 5. Chemical Safety Testing.

Benefit # 1. Normal Physiology and Development:

Transgenic animals can be specifically designed to allow the study of how genes are regulated and how they affect the normal functioning of the body and its development.

For example, the study of complex factors involved in growth such as insulin likes growth factors.

Benefit # 2. Study of Disease:

Many transgenic animals are designed to increase the understanding of that how genes contribute to the development of diseases such as cancer, cystic fibrosis, rheumatoid arthritis and Alzheimer.

These are specially made to serve as models for human diseases, so that investigation of new treatments for diseases is made possible.

Benefit # 3. Biological Products:

Human disease can be treated by medicines that contain biological products.

(a) Transgenic animals that produce useful biological products can be created by the introduction of the portion of the DNA or genes that codes for a particular product such as human protein (alpha-1-antitrypsin) which is used to treat emphysema.

(b) Similar attempts are being made for the treatment of phenylketonuria (PKU) and cystic fibrosis. For example, the first transgenic cow Rosie produced human protein enriched milk (2.4 g/L) in 1997. The milk contained the human alpha lactalbumin and was nutritionally a more balanced product for human babies than natural cow milk.

Benefit # 4. Vaccine Safety:

Transgenic mice are being used in testing the safety of vaccines before they are used in humans, e.g., polio vaccine.

These animals are also used for the toxicity or safety testing procedures. If found reliable and successful they could replace the use of monkeys in order to test the safety of batches of the vaccine.

Benefit # 5. Chemical Safety Testing:

Transgenic animals are made to carry the genes, which make them more sensitive to the toxic substances than the non-transgenic ones. They are then exposed to toxic substances and effects are studied. This is known as toxicity/safety testing.


The process of genetically engineering mammals is a slow, tedious, and expensive process. [2] As with other genetically modified organisms (GMOs), first genetic engineers must isolate the gene they wish to insert into the host organism. This can be taken from a cell containing the gene [3] or artificially synthesised. [4] If the chosen gene or the donor organism's genome has been well studied it may already be accessible from a genetic library. The gene is then combined with other genetic elements, including a promoter and terminator region and usually a selectable marker. [5]

A number of techniques are available for inserting the isolated gene into the host genome. With animals DNA is generally inserted into using microinjection, where it can be injected through the cell's nuclear envelope directly into the nucleus, or through the use of viral vectors. [6] The first transgenic animals were produced by injecting viral DNA into embryos and then implanting the embryos in females. [7] It is necessary to ensure that the inserted DNA is present in the embryonic stem cells. [8] The embryo would develop and it would be hoped that some of the genetic material would be incorporated into the reproductive cells. Then researchers would have to wait until the animal reached breeding age and then offspring would be screened for presence of the gene in every cell, using PCR, Southern hybridization, and DNA sequencing. [9]

New technologies are making genetic modifications easier and more precise. [2] Gene targeting techniques, which creates double-stranded breaks and takes advantage on the cells natural homologous recombination repair systems, have been developed to target insertion to exact locations. Genome editing uses artificially engineered nucleases that create breaks at specific points. There are four families of engineered nucleases: meganucleases, [10] [11] zinc finger nucleases, [12] [13] transcription activator-like effector nucleases (TALENs), [14] [15] and the Cas9-guideRNA system (adapted from CRISPR). [16] [17] TALEN and CRISPR are the two most commonly used and each has its own advantages. [18] TALENs have greater target specificity, while CRISPR is easier to design and more efficient. [18] The development of the CRISPR-Cas9 gene editing system has effectively halved the amount of time needed to develop genetically modified animals. [19]

Humans have domesticated animals since around 12,000 BCE, using selective breeding or artificial selection (as contrasted with natural selection). The process of selective breeding, in which organisms with desired traits (and thus with the desired genes) are used to breed the next generation and organisms lacking the trait are not bred, is a precursor to the modern concept of genetic modification [20] : 1 Various advancements in genetics allowed humans to directly alter the DNA and therefore genes of organisms. In 1972 Paul Berg created the first recombinant DNA molecule when he combined DNA from a monkey virus with that of the lambda virus. [21] [22]

In 1974 Rudolf Jaenisch created a transgenic mouse by introducing foreign DNA into its embryo, making it the world's first transgenic animal. [23] [24] However it took another eight years before transgenic mice were developed that passed the transgene to their offspring. [25] [26] Genetically modified mice were created in 1984 that carried cloned oncogenes, predisposing them to developing cancer. [27] Mice with genes knocked out (knockout mouse) were created in 1989. The first transgenic livestock were produced in 1985 [28] and the first animal to synthesise transgenic proteins in their milk were mice, [29] engineered to produce human tissue plasminogen activator in 1987. [30]

The first genetically modified animal to be commercialised was the GloFish, a Zebra fish with a fluorescent gene added that allows it to glow in the dark under ultraviolet light. [31] It was released to the US market in 2003. [32] The first genetically modified animal to be approved for food use was AquAdvantage salmon in 2015. [33] The salmon were transformed with a growth hormone-regulating gene from a Pacific Chinook salmon and a promoter from an ocean pout enabling it to grow year-round instead of only during spring and summer. [34]

GM mammals are created for research purposes, production of industrial or therapeutic products, agricultural uses or improving their health. There is also a market for creating genetically modified pets. [35]

Medicine Edit

Mammals are the best models for human disease, making genetic engineered ones vital to the discovery and development of cures and treatments for many serious diseases. Knocking out genes responsible for human genetic disorders allows researchers to study the mechanism of the disease and to test possible cures. Genetically modified mice have been the most common mammals used in biomedical research, as they are cheap and easy to manipulate. Pigs are also a good target as they have a similar body size and anatomical features, physiology, pathophysiological response and diet. [36] Nonhuman primates are the most similar model organisms to humans, but there is less public acceptance towards using them as research animals. [37] In 2009, scientists announced that they had successfully transferred a gene into a primate species (marmosets) and produced a stable line of breeding transgenic primates for the first time. [38] [39] Their first research target for these marmosets was Parkinson's disease, but they were also considering amyotrophic lateral sclerosis and Huntington's disease. [40]

Human proteins expressed in mammals are more likely to be similar to their natural counterparts than those expressed in plants or microorganisms. Stable expression has been accomplished in sheep, pigs, rats and other animals. In 2009, the first human biological drug produced from such an animal, a goat., was approved. The drug, ATryn, is an anticoagulant which reduces the probability of blood clots during surgery or childbirth was extracted from the goat's milk. [41] Human alpha-1-antitrypsin is another protein that is used in treating humans with this deficiency. [42] Another area is in creating pigs with greater capacity for human organ transplants (xenotransplantation). Pigs have been genetically modified so that their organs can no longer carry retroviruses [43] or have modifications to reduce the chance of rejection. [44] [45] Pig lungs from genetically modified pigs are being considered for transplantation into humans. [46] [47] There is even potential to create chimeric pigs that can carry human organs. [36] [48]

Livestock Edit

Livestock are modified with the intention of improving economically important traits such as growth-rate, quality of meat, milk composition, disease resistance and survival. Animals have been engineered to grow faster, be healthier [49] and resist diseases. [50] Modifications have also improved the wool production of sheep and udder health of cows. [1]

Goats have been genetically engineered to produce milk with strong spiderweb-like silk proteins in their milk. [51] The goat gene sequence has been modified, using fresh umbilical cords taken from kids, in order to code for the human enzyme lysozyme. Researchers wanted to alter the milk produced by the goats, to contain lysozyme in order to fight off bacteria causing diarrhea in humans. [52]

Enviropig was a genetically enhanced line of Yorkshire pigs in Canada created with the capability of digesting plant phosphorus more efficiently than conventional Yorkshire pigs. [53] [54] The A transgene construct consisting of a promoter expressed in the murine parotid gland and the Escherichia coli phytase gene was introduced into the pig embryo by pronuclear microinjection. [55] This caused the pigs to produce the enzyme phytase, which breaks down the indigestible phosphorus, in their saliva. [53] [56] As a result, they excrete 30 to 70% less phosphorus in manure depending upon the age and diet. [53] [56] The lower concentrations of phosphorus in surface runoff reduces algal growth, because phosphorus is the limiting nutrient for algae. [53] Because algae consume large amounts of oxygen, excessive growth can result in dead zones for fish. Funding for the Enviropig program ended in April 2012, [57] and as no new partners were found the pigs were killed. [58] However, the genetic material will be stored at the Canadian Agricultural Genetics Repository Program. In 2006, a pig was engineered to produce omega-3 fatty acids through the expression of a roundworm gene. [59]

In 1990, the world's first transgenic bovine, Herman the Bull, was developed. Herman was genetically engineered by micro-injected embryonic cells with the human gene coding for lactoferrin. The Dutch Parliament changed the law in 1992 to allow Herman to reproduce. Eight calves were born in 1994 and all calves inherited the lactoferrin gene. [60] With subsequent sirings, Herman fathered a total of 83 calves. [61] Dutch law required Herman to be slaughtered at the conclusion of the experiment. However the Dutch Agriculture Minister at the time, Jozias van Aartsen, granted him a reprieve provided he did not have more offspring after public and scientists rallied to his defence. [62] Together with cloned cows named Holly and Belle, he lived out his retirement at Naturalis, the National Museum of Natural History in Leiden. [62] On 2 April 2004, Herman was euthanised by veterinarians from the University of Utrecht because he suffered from osteoarthritis. [63] [62] At the time of his death Herman was one of the oldest bulls in the Netherlands. [63] Herman's hide has been preserved and mounted by taxidermists and is permanently on display in Naturalis. They say that he represents the start of a new era in the way man deals with nature, an icon of scientific progress, and the subsequent public discussion of these issues. [63]

In October 2017, Chinese scientists announced they used CRISPR technology to create of a line of pigs with better body temperature regulation, resulting in about 24% less body fat than typical livestock. [64]

Researchers have developed GM dairy cattle to grow without horns (sometimes referred to as "polled") which can cause injuries to farmers and other animals. DNA was taken from the genome of Red Angus cattle, which is known to suppress horn growth, and inserted into cells taken from an elite Holstein bull called "Randy". Each of the progeny will be a clone of Randy, but without his horns, and their offspring should also be hornless. [65] In 2011, Chinese scientists generated dairy cows genetically engineered with genes from human beings to produce milk that would be the same as human breast milk. [66] This could potentially benefit mothers who cannot produce breast milk but want their children to have breast milk rather than formula. [67] [68] The researchers claim these transgenic cows to be identical to regular cows. [69] Two months later, scientists from Argentina presented Rosita, a transgenic cow incorporating two human genes, to produce milk with similar properties as human breast milk. [70] In 2012, researchers from New Zealand also developed a genetically engineered cow that produced allergy-free milk. [71]

Research Edit

Scientists have genetically engineered several organisms, including some mammals, to include green fluorescent protein (GFP), for research purposes. [72] GFP and other similar reporting genes allow easy visualisation and localisation of the products of the genetic modification. [73] Fluorescent pigs have been bred to study human organ transplants, regenerating ocular photoreceptor cells, and other topics. [74] In 2011 green-fluorescent cats were created to find therapies for HIV/AIDS and other diseases [75] as feline immunodeficiency virus (FIV) is related to HIV. [76] Researchers from the University of Wyoming have developed a way to incorporate spiders' silk-spinning genes into goats, allowing the researchers to harvest the silk protein from the goats’ milk for a variety of applications. [77]

Conservation Edit

Genetic modification of the myxoma virus has been proposed to conserve European wild rabbits in the Iberian peninsula and to help regulate them in Australia. To protect the Iberian species from viral diseases, the myxoma virus was genetically modified to immunize the rabbits, while in Australia the same myxoma virus was genetically modified to lower fertility in the Australian rabbit population. [78] There have also been suggestions that genetic engineering could be used to bring animals back from extinction. It involves changing the genome of a close living relative to resemble the extinct one and is currently being attempted with the passenger pigeon. [79] Genes associated with the woolly mammoth have been added to the genome of an African Elephant, although the lead researcher says he has no intention of using live elephants. [80]

Humans Edit

Gene therapy [81] uses genetically modified viruses to deliver genes which can cure disease in humans. Although gene therapy is still relatively new, it has had some successes. It has been used to treat genetic disorders such as severe combined immunodeficiency, [82] and Leber's congenital amaurosis. [83] Treatments are also being developed for a range of other currently incurable diseases, such as cystic fibrosis, [84] sickle cell anemia, [85] Parkinson's disease, [86] [87] cancer, [88] [89] [90] diabetes, [91] heart disease [92] and muscular dystrophy. [93] These treatments only affect somatic cells, meaning any changes would not be inheritable. Germline gene therapy results in any change being inheritable, which has raised concerns within the scientific community. [94] [95] In 2015, CRISPR was used to edit the DNA of non-viable human embryos. [96] [97] In November 2018, He Jiankui announced that he had edited the genomes 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 and that they 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. [98]

Genetically modified fish are used for scientific research, as pets and as a food source. Aquaculture is a growing industry, currently providing over half the consumed fish worldwide. [99] Through genetic engineering it is possible to increase growth rates, reduce food intake, remove allergenic properties, increase cold tolerance and provide disease resistance.

Detecting pollution Edit

Fish can also be used to detect aquatic pollution or function as bioreactors. [100] Several groups have been developing zebrafish to detect pollution by attaching fluorescent proteins to genes activated by the presence of pollutants. The fish will then glow and can be used as environmental sensors. [101] [102]

Pets Edit

The GloFish is a brand of genetically modified fluorescent zebrafish with bright red, green, and orange fluorescent color. It was originally developed by one of the groups to detect pollution, but is now part of the ornamental fish trade, becoming the first genetically modified animal to become publicly available as a pet when it was introduced for sale in 2003. [103]

Research Edit

GM fish are widely used in basic research in genetics and development. Two species of fish, zebrafish and medaka, are most commonly modified because they have optically clear chorions (membranes in the egg), rapidly develop, and the 1-cell embryo is easy to see and microinject with transgenic DNA. [104] Zebrafish are model organisms for developmental processes, regeneration, genetics, behaviour, disease mechanisms and toxicity testing. [105] Their transparency allows researchers to observe developmental stages, intestinal functions and tumour growth. [106] [107] The generation of transgenic protocols (whole organism, cell or tissue specific, tagged with reporter genes) has increased the level of information gained by studying these fish. [108]

Growth Edit

GM fish have been developed with promoters driving an over-production of "all fish" growth hormone for use in the aquaculture industry to increase the speed of development and potentially reduce fishing pressure on wild stocks. This has resulted in dramatic growth enhancement in several species, including salmon, [109] trout [110] and tilapia. [111]

AquaBounty Technologies have produced a salmon that can mature in half the time as wild salmon. [112] The fish is an Atlantic salmon with a Chinook salmon (Oncorhynchus tshawytscha) gene inserted. This allows the fish to produce growth hormones all year round compared to the wild-type fish that produces the hormone for only part of the year. [113] The fish also has a second gene inserted from the eel-like ocean pout that acts like an "on" switch for the hormone. [113] Pout also have antifreeze proteins in their blood, which allow the GM salmon to survive near-freezing waters and continue their development. [114] The wild-type salmon takes 24 to 30 months to reach market size (4–6 kg) whereas the producers of the GM salmon say it requires only 18 months for the GM fish to achieve this. [114] [115] [116] In November 2015, the FDA of the USA approved the AquAdvantage salmon for commercial production, sale and consumption, [117] the first non-plant GMO food to be commercialised. [118]

AquaBounty say that to prevent the genetically modified fish inadvertently breeding with wild salmon, all the fish will be female and reproductively sterile, [116] although a small percentage of the females may remain fertile. [113] Some opponents of the GM salmon have dubbed it the "Frankenfish". [113] [119]

Research Edit

In biological research, transgenic fruit flies (Drosophila melanogaster) are model organisms used to study the effects of genetic changes on development. [120] Fruit flies are often preferred over other animals due to their short life cycle and low maintenance requirements. It also has a relatively simple genome compared to many vertebrates, with typically only one copy of each gene, making phenotypic analysis easy. [121] Drosophila have been used to study genetics and inheritance, embryonic development, learning, behavior, and aging. [122] Transposons (particularly P elements) are well developed in Drosophila and provided an early method to add transgenes to their genome, although this has been taken over by more modern gene-editing techniques. [123]

Population control Edit

Due to their significance to human health, scientists are looking at ways to control mosquitoes through genetic engineering. Malaria-resistant mosquitoes have been developed in the laboratory. [124] by inserting a gene that reduces the development of the malaria parasite [125] and then use homing endonucleases to rapidly spread that gene throughout the male population (known as a gene drive). [126] This has been taken further by swapping it for a lethal gene. [127] [128] In trials the populations of Aedes aegypti mosquitoes, the single most important carrier of dengue fever and Zika virus, were reduced by between 80% and by 90%. [129] [130] [128] Another approach is to use the sterile insect technique, whereby males genetically engineered to be sterile out compete viable males, to reduce population numbers. [131]

Other insect pests that make attractive targets are moths. Diamondback moths cause US$4 to $5 billion of damage a year worldwide. [132] The approach is similar to the mosquitoes, where males transformed with a gene that prevents females from reaching maturity will be released. [133] They underwent field trials in 2017. [132] Genetically modified moths have previously been released in field trials. [134] A strain of pink bollworm that were sterilised with radiation were genetically engineered to express a red fluorescent protein making it easier for researchers to monitor them. [135]

Industry Edit

Silkworm, the larvae stage of Bombyx mori, is an economically important insect in sericulture. Scientists are developing strategies to enhance silk quality and quantity. There is also potential to use the silk producing machinery to make other valuable proteins. [136] Proteins expressed by silkworms include human serum albumin, human collagen α-chain, mouse monoclonal antibody and N-glycanase. [137] Silkworms have been created that produce spider silk, a stronger but extremely difficult to harvest silk, [138] and even novel silks. [139]

Attempts to produce genetically modified birds began before 1980. [140] Chickens have been genetically modified for a variety of purposes. This includes studying embryo development, [141] preventing the transmission of bird flu [142] and providing evolutionary insights using reverse engineering to recreate dinosaur-like phenotypes. [143] A GM chicken that produces the drug Kanuma, an enzyme that treats a rare condition, in its egg passed regulatory approval in 2015. [144]

Disease control Edit

One potential use of GM birds could be to reduce the spread of avian disease. Researchers at Roslin Institute have produced a strain of GM chickens (Gallus gallus domesticus) that does not transmit avian flu to other birds however, these birds are still susceptible to contracting it. The genetic modification is an RNA molecule that prevents the virus reproduction by mimicking the region of the flu virus genome that controls replication. It is referred to as a "decoy" because it diverts the flu virus enzyme, the polymerase, from functions that are required for virus replication. [145]

Evolutionary insights Edit

A team of geneticists led by University of Montana paleontologist Jack Horner is seeking to modify a chicken to express several features present in ancestral maniraptorans but absent in modern birds, such as teeth and a long tail, [146] creating what has been dubbed a 'chickenosaurus'. [147] Parallel projects have produced chicken embryos expressing dinosaur-like skull, [148] leg, [143] and foot [149] anatomy.

Genetically modified frogs, in particular Xenopus laevis and Xenopus tropicalis, are used in development biology. GM frogs can also be used as pollution sensors, especially for endocrine disrupting chemicals. [150] There are proposals to use genetic engineering to control cane toads in Australia. [151] [152]

The nematode Caenorhabditis elegans is one of the major model organisms for researching molecular biology. [153] RNA interference (RNAi) was discovered in C elegans [154] and could be induced by simply feeding them bacteria modified to express double stranded RNA. [155] It is also relatively easy to produce stable transgenic nematodes and this along with RNAi are the major tools used in studying their genes. [156] The most common use of transgenic nematodes has been studying gene expression and localisation by attaching reporter genes. Transgenes can also be combined with RNAi to rescue phenotypes, altered to study gene function, imaged in real time as the cells develop or used to control expression for different tissues or developmental stages. [156] Transgenic nematodes have been used to study viruses, [157] toxicology, [158] and diseases [159] [160] and to detect environmental pollutants. [161]

Systems have been developed to create transgenic organisms in a wide variety of other animals. The gene responsible for Albinism in sea cucumbers has been found and used to engineer white sea cucumbers, a rare delicacy. The technology also opens the way to investigate the genes responsible for some of the cucumbers more unusual traits, including hibernating in summer, eviscerating their intestines, and dissolving their bodies upon death. [162] Flatworms have the ability to regenerate themselves from a single cell. [163] Until 2017 there was no effective way to transform them, which hampered research. By using microinjection and radiation scientist have now created the first genetically modified flatworms. [164] The bristle worm, a marine annelid, has been modified. It is of interest due to its reproductive cycle being synchronised with lunar phases, regeneration capacity and slow evolution rate. [165] Cnidaria such as Hydra and the sea anemone Nematostella vectensis are attractive model organisms to study the evolution of immunity and certain developmental processes. [166] Other organisms that have been genetically modified include snails, [167] geckos, turtles, [168] crayfish, oysters, shrimp, clams, abalone [169] and sponges. [170]


8.8: Transgenic organisms - Biology

A new brand of farming is emerging from the research and development labs of several universities and small biotechnology companies-so new they're even changing the spelling to "pharming."

Pharming is the production of human pharmaceuticals in farm animals that is presently in the development stage with possible commercialization by the year 2000. It has been gaining application among biotechnologists since the development of transgenic "super mice" in 1982 and the development of the first mice to produce a human drug, tPA (tissue plasminogen activator to treat blood clots), in 1987. Transgenic organisms have been modified by genetic engineering to contain DNA from an external source. The first drugs produced by this approach are about to enter clinical trials as part of the FDA review process. These transgenic animals will likely be raised by the pharmaceutical companies and will certainly be kept separate from the food supply.

Genetic Engineering

During the 1970s, advances in DNA manipulation techniques provided a significant, economical alternative source for many drugs made of protein. Previously, these protein drugs were available in extremely limited supplies for example, human cadavers were the source for human growth hormone, and insulin to treat diabetes was collected from slaughtered pigs.

By genetic engineering, the DNA gene for a protein drug of interest can be transferred into another organism that will produce large amounts of the drug. This technique (illustrated in Figure 1), can be used to impart new production characteristics to an organism, as well as to trigger the production of a protein drug:

1) The gene of interest is isolated on a strand of DNA.

2) DNA is cut at specific points by restriction enzymes. The enzymes recognize certain sequences of bases on the DNA strand and cut where those sequences appear.

3) The cut DNA joins with a vector , which may be a virus or part of a bacterial cell called a plasmid. The vector carries the gene of interest into the organism that will produce the protein.

4) Transformation occurs when the gene carried by the vector is incorporated into the DNA of another organism where it initiates the action desired (production of a drug, etc.).

The first successful products of the genetic engineering process were protein drugs like insulin and growth hormone. These drugs do not have to be produced by mammals to be active in mammals. An inexpensive, easy-to-grow culture of genetically engineered bacteria like the common E. coli can manufacture these protein drugs.

Other human drugs, such as tPA for blood clots, erythropoietin for anemia, and blood clotting factors VIII and IX for hemophilia, require modifications that only cells of higher organisms like mammals can provide. The higher costs of maintaining mammalian cell cultures that produce only small amounts of the drugs have been an enormous barrier to the commercial development of this type of cell culture production method.

Animal Pharming

By genetic engineering, the DNA gene for a protein drug of interest can be transferred into another organism for production. Which organism to use for production is a technical and economic decision.

For certain protein drugs that require complex modifications or are needed in large supply, production in transgenic animals seems most efficient. The farm animal becomes a production facility with many advantages-it is reproducible, has a flexible production capacity through the number of animals bred, and maintains its own fuel supply. Best of all, in most animal drug production, the drug is delivered from the animal in a very convenient form-in the milk!

Procedure

A transgenic animal for pharmaceutical production should (1) produce the desired drug at high levels without endangering its own health and (2) pass its ability to produce the drug at high levels to its offspring.

The current strategy to achieve these objectives is to couple the DNA gene for the protein drug with a DNA signal directing production in the mammary gland. The new gene, while present in every cell of the animal, functions only in the mammary gland so the protein drug is made only in the milk. Since the mammary gland and milk are essentially "outside" the main life support systems of the animal, there is virtually no danger of disease or harm to the animal in making the "foreign" protein drug.

After the DNA gene for the protein drug has been coupled with the mammary directing signal, this DNA is injected into fertilized cow, sheep, goat, or mouse embryos with the aid of a very fine needle, a tool called a micromanipulator, and a microscope (Figure 2). The injected embryos are then implanted into recipient surrogate mothers where, hopefully, they survive and are born normally.

Commercialization Issues

Success in creating a transgenic animal that can produce the drug is far from guaranteed. About 10 to 30 percent of mouse embryos produce transgenics, but less than 5 percent of goats, sheep, or cows do. Production of the drug is measured during lactation after the animal is raised to maturity and bred. Because of the long time periods involved and low success rates, developing transgenic animals is currently very expensive, as the dollar amounts in Table 1 indicate.

Although most protein drugs are made in milk, a notable exception is human hemoglobin that is being made in swine blood to provide a blood substitute for human transfusions. Because hemoglobin is naturally a blood protein, it is likely to be one of few exceptions to the usual method of production in milk. Furthermore, the economics of blood production are less favorable, because to recover human hemoglobin, the animal producing it must be slaughtered.

Drugs currently made by or being developed in transgenic animals are listed in Table 1. Notice that pharming is expected to increase the value of animals dramatically. In general, animal pharming is considered to be 5 to 10 times more economical on a continuing basis and 2 to 3 times cheaper in startup costs than cell culture production methods.

Regulatory and Ethical Issues

Production of human pharmaceuticals in farm animals has many technical barriers to overcome, although most technologists agree that these technical difficulties will be easily resolved in the 1990s. As a production method, animal pharming is entirely unprecedented and is likely to undergo significant evaluation by the Food and Drug Administration (FDA). Human drugs purified from animal milk or blood are likely to require exceptional levels of safety testing before animal and human health concerns are addressed to the satisfaction of consumers.

At a more fundamental level, many people are genuinely concerned about animal welfare and biotechnology's redefinition of the relationship between humans and animals. Genetic engineering and transgenic animal research are essentially human endeavors to improve the availability, quality, and safety of drugs to enhance human health and to improve animal health. Animal breeding has gone on for centuries, but the ability to change the DNA of the animal brings breeding to a revolutionary new level.

Information Sources

Frank Gwazdauskas, professor, dairy science department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0315.

"See How They (Don't) Grow." Successful Farming. March 1991, p. 33.

"Transgenic Animals in the Production of Therapeutic Proteins." Biotechnology International. Century Press, 1992, p. 317.

"Transgenic Pharming Advances." Bio/Technology. May 1992, p. 498.

"Whole Animals for Wholesale Protein Production." Bio/Technology. August 1992, p. 863. Table 1


Written by David F. Betsch, Ph.D., Biotechnology Training Programs, Inc. Edited by Glenda D. Webber, Iowa State University Office of Biotechnology.


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GMOs in agriculture

Genetically modified (GM) foods were first approved for human consumption in the United States in 1994, and by 2014–15 about 90 percent of the corn, cotton, and soybeans planted in the United States were GM. By the end of 2014, GM crops covered nearly 1.8 million square kilometres (695,000 square miles) of land in more than two dozen countries worldwide. The majority of GM crops were grown in the Americas.

Engineered crops can dramatically increase per area crop yields and, in some cases, reduce the use of chemical insecticides. For example, the application of wide-spectrum insecticides declined in many areas growing plants, such as potatoes, cotton, and corn, that were endowed with a gene from the bacterium Bacillus thuringiensis, which produces a natural insecticide called Bt toxin. Field studies conducted in India in which Bt cotton was compared with non-Bt cotton demonstrated a 30–80 percent increase in yield from the GM crop. This increase was attributed to marked improvement in the GM plants’ ability to overcome bollworm infestation, which was otherwise common. Studies of Bt cotton production in Arizona, U.S., demonstrated only small gains in yield—about 5 percent—with an estimated cost reduction of $25–$65 (USD) per acre owing to decreased pesticide applications. In China, where farmers first gained access to Bt cotton in 1997, the GM crop was initially successful. Farmers who had planted Bt cotton reduced their pesticide use by 50–80 percent and increased their earnings by as much as 36 percent. By 2004, however, farmers who had been growing Bt cotton for several years found that the benefits of the crop eroded as populations of secondary insect pests, such as mirids, increased. Farmers once again were forced to spray broad-spectrum pesticides throughout the growing season, such that the average revenue for Bt growers was 8 percent lower than that of farmers who grew conventional cotton. Meanwhile, Bt resistance had also evolved in field populations of major cotton pests, including both the cotton bollworm (Helicoverpa armigera) and the pink bollworm (Pectinophora gossypiella).

Other GM plants were engineered for resistance to a specific chemical herbicide, rather than resistance to a natural predator or pest. Herbicide-resistant crops (HRC) have been available since the mid-1980s these crops enable effective chemical control of weeds, since only the HRC plants can survive in fields treated with the corresponding herbicide. Many HRCs are resistant to glyphosate (Roundup), enabling liberal application of the chemical, which is highly effective against weeds. Such crops have been especially valuable for no-till farming, which helps prevent soil erosion. However, because HRCs encourage increased application of chemicals to the soil, rather than decreased application, they remain controversial with regard to their environmental impact. In addition, in order to reduce the risk of selecting for herbicide-resistant weeds, farmers must use multiple diverse weed-management strategies.

Another example of a GM crop is “golden” rice, which originally was intended for Asia and was genetically modified to produce almost 20 times the beta-carotene of previous varieties. Golden rice was created by modifying the rice genome to include a gene from the daffodil Narcissus pseudonarcissus that produces an enzyme known as phyotene synthase and a gene from the bacterium Erwinia uredovora that produces an enzyme called phyotene desaturase. The introduction of these genes enabled beta-carotene, which is converted to vitamin A in the human liver, to accumulate in the rice endosperm—the edible part of the rice plant—thereby increasing the amount of beta-carotene available for vitamin A synthesis in the body. In 2004 the same researchers who developed the original golden rice plant improved upon the model, generating golden rice 2, which showed a 23-fold increase in carotenoid production.

Another form of modified rice was generated to help combat iron deficiency, which impacts close to 30 percent of the world population. This GM crop was engineered by introducing into the rice genome a ferritin gene from the common bean, Phaseolus vulgaris, that produces a protein capable of binding iron, as well as a gene from the fungus Aspergillus fumigatus that produces an enzyme capable of digesting compounds that increase iron bioavailability via digestion of phytate (an inhibitor of iron absorption). The iron-fortified GM rice was engineered to overexpress an existing rice gene that produces a cysteine-rich metallothioneinlike (metal-binding) protein that enhances iron absorption.

A variety of other crops modified to endure the weather extremes common in other parts of the globe are also in production.


Watch the video: Trangenes and Transgenic Organisms (December 2021).