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A transgenic organism is an organism that has had its genome manipulated(16), using recombinant DNA techniques to introduce new characteristics into the organism that was not there previously, these characteristics are passed down to the offspring and will continue though the gene pool.
These genetically modified organisms are used in the search to find new cures for difficult diseases, or the increase in production yields of crops and other organic related products that feed and improve our lives.
However, the scientists who are genetically manipulating these organisms are closely monitored by their local government and have to adhere to very strict guide lines and regulations. If scientists would like to attempt to create a new transgenic organism they must first make an appeal to their government or their superiors with their theories on what they hope to achieve and what will mankind benefit from this organism. Regardless of all regulations to help prevent any harmful incidents there is still a lot of controversy; on this subject as people protest against it, claim that the scientists are playing god and that the organisms should be allowed to evolve on their own.(15)
A brief History
In Brinster 1974, the first chimeric mice were produced, by combining two different embryos during early development (eight cells) from two different strains of mice to form a single embryo which was able to develop into an adult, showing characteristics of each strain. Soon after this, it has been attempted with other animals e.g. a sheep and a goat to create a 'geep' (1982). (18)
Gordon and Ruddle (1981) were the first to describe Transgenesis, by using DNA microinjection of mice ova. Various other species such as rats, birds, rabbits, pigs, sheep and fish soon followed.
The use of Transgenesis has gained more interest amongst biotechnologists since the development of the 'super mice', a transgenic organism developed in 1982 which produced a human drug, TPA (tissue plaminogen activator to treat blood clots) in 1987.
Transgenesis is the introduction of new DNA in to an organism using recombinant DNA techniques. The term Transgenic Organism refers to an organism that has had a deliberate modification to its genome. The foreign DNA is introduced into the organism via recombinant DNA technology and must then be distributed though out the germ line, in order to ensure that the modified genetic material is present in every cell, including germ cells. Once the germ line is completely altered the modified genetic material can be passed on to its offspring via normal reproduction. (17)
If the somatic cell line is only modified then the traits will only be present in that individual and not its offspring.
Transgenesis is not to be confused with cloning, although very similar, cloning involves producing an exact copy of the original organism, cloning does not necessarily involve the manipulating of genes. (18)
Uses for Transgenesis
Gene therapy, the alteration of the genetic make-up of an organism in the attempt to cure an inborn error of metabolism (i.e. cure an inherited disease). This is generally only carried out with somatic cell thus it will only affect the modified organism. (18)
Toxicology, the use of responsive test animals in the study of poisons and toxins and their effects on living organisms. (18)
Molecular biology, analysing the regulation of gene expression. (18)
Pharmaceutical Industry ("Pharming"), the production of drugs, pharmaceutical proteins and product efficiency tests. (18)
Bio technology, as producers of specific proteins. (19)
Genetic Engineering, to increase the production yield of milk, meat production, the modification of live stock in agriculture or cloning procedures to reproduce specific blood lines. (19)
To speed up evolution by taking an existing gene and spread it, this is to improve the organism or to help aid modification. (18)
The study of disease:
Transgenic organisms have been use for the study of diseases and their treatments; they do this by inserting a transgene of human DNA and the disease (Viral or bacterial) and add or subtract DNA strands until a result is reached.
Method of alteration
Human disease equivalent
Introduction of mutant collagen gene into wild type mice
Nuclear microinjection of inducible minigene
Inactivation of mouse gene encoding hypoxanthine-guanine phosphoribosyl transferase (HPRT)
Insertion of retrovirus into HPRT locus in embryonic stem cells
Mutation at locus for X-linked muscular dystrophy
Male mutagenesis followed by identification of female carriers
X-linked muscular dystrophy
Introduction of activated humanras and c-myc oncogenes
Nuclear microinjection of inducible minigene
Induction of malignancy
Introduction of mutant (Z)allele of human alpha -1-antitrypsin gene
Microinjection of DNA fragment bearing mutant allele
Introduction of HIV tat gene
Microinjection of DNA fragment
Introduction of beta-globin sickle gene
Introduction of mouse renin gene
Introduction of (beta)-amyloid protein precursor (APP gene)
A table representing witch gene is altered, the method used and the equivalent disease in humans. (18)
Transgenic crops have now been applied to a lot of our very important crops for example rice, cotton, soybean, oilseeds rape and a large variety of vegetables like potatoes, tomato, cabbage and lettuce. There have also been a number of new crops that have been produced using genes from bacteria and viruses that will help the plant be more resistant to certain types of diseases and pests and be more tolerant to herbicide, allowing the herbicides to target weeds more effectively. (18)
These transgenic crops that have been integrated with a resistance to pests and diseases allow farmers to uses less pesticides and herbicides and thus they do not affect the ph of the soil and the water tables. (18)
Transgenic manipulations are also being used to increase the nutrition value in the crops as well as the production yield and quality of the products. (18)
The main use of Transgenesis is the use of it in livestock by altering their biochemistry, improving the hormonal balance and altering their protein productions.
These scientists hopes to create a healthier, leaner, faster growing animal that requires less food, as well as animals that will help produce useable materials and help prevent global warming.
Some examples of transgenic animals:
Goats that can produce the same proteins that are found spider webs. (4)
Nexia Biotechnologies in Quebec, Canada have designed a goat the produces spider silk proteins in its milk. The silk is used in the research for light weight bullet proof vests and in use in the medical world as artificial tendons, ligament and limbs and as ultra-thin sutures for eye- or neurosurgery. (5)
Fluorescent monkeys created in the central institute for experimental animals in Japan are used in possibly finding a cure for the diseases Parkinson's and Multiple sclerosis. To give the monkeys the fluorescent gene, the gene is taken out of the jelly fish Aequorea Victoria. (11)
The GloFish which is a zebra fish (Danio reio) was created in the national university of Singapore in 1999 by Dr. Zhiyuan Gong and his colleagues for the propose of detecting pollution in the waters by glowing when in contact with environmental toxins. The GloFish has become a novelty pet and over two hundred million have been sold in America over the last eleven years. (7)
Fluorescent cats are being used in the hopes of finding a cure for aids. These cats were infected with FIV (feline immunodeficiency virus) and the virus had trouble replicating, the reason for this phenomenon is still being researched. These cats were created by Eric Poeschla at the mayo clinic in Rochester in Minnesota. (12)
A modified line of Yorkshire pigs know as Enviropigs have been altered to produce less phosphate in their faecal matter and thus help prevent pollution and global warming. The pigs were developed in the University of Guelph and produce 20% to 60% phosphate as opposed to 50% to 75%. (2)
The DNA that is inserted into the organism is known as the transgene.
Conventional DNA recombinant techniques are used to build the transgene so that the desired trait will be expressed in the correct location. Typical transgenes contain nucleotide sequences which are corresponding to the gene of interest, once all the necessary components are acquired for efficient expression of that trait, including a transcription-initiation site, the 5' untranslated region, a translation-initiating codon, the codon region, a stop codon, the 3' untranslated region, a polyadenylation site and a promoter. Different types of promoters can be used to cause gene expression in specific parts of the organism or the entire organism.
Promoter and where they are expressed in organisms (18)
GENE EXPRESSION IN
many tissues of the transgenic animal
simian virus 40 T antigen promoter
many tissues of the transgenic animal
adipocyte P2 promoter
myosin light-chain promoter
islets of Langerhans beta cells
In pharmaceutical production it is very convenient to have the trait expressed the mammary glands, the product will then be present in the milk of the organism.
Three types of introducing exogenous DNA into animal cells
The three main methods for the creation of transgenic organisms are DNA microinjection, embryonic stem cell-meditated gene transfer and retrovirus-meditated gene transfer.
This method involves the injection of the gene construct (the genetic code) from another organism into a pronucleus of a fertilised ovum. The introduction of this DNA could lead to the over or under expression of a specific trait or the expression of an entirely new species.
The DNA construct is injected into the male pronucleus though a fine glass needle (the male pronucleus is provided by sperm before it bonds to the nucleus of the ovum). The diameter of the glass needle is 0.75µm and that of the ovum is 70µm. The bio technician uses a binocular microscope at a magnification of 200 xs to perform the manipulations. (18)
However, the insertion of the DNA is a random process and the probability of the gene that was introduced will not insert itself on the site of the host DNA that will allow the trait to be expressed.
This method is the most common method at present and is generally more successful with laboratory animals than with farm animals.
The efficiency with farm animals is rather low, see appendix 3. (18)
Figures in parentheses are percent efficiency compared to original number of ova injected. (18)
Number of ova
Number of offspring
Number of transgenic
Embryonic stem cell / meditated gene transfer
This method requires prior insertion of a desired DNA strands via homologous recombination into an invitro (outside of the body, in a laboratory) culture embryonic stem (ES) cells (Stem cells are cells that are indifferent and have the ability to change into any type of cell, be it somatic or germ cells). The Stem cells are then integrated into an embryo during the blastocyst stage (the stage of development five days after fertilisation), this then results in a chimerical organism. (18)
ES cell-meditated gene transfer is the preferred method for gene inactivation the so called knock-out method.
This method is used in the study of genetic control of developmental processes. This technique is used predominantly with mice
It also has the advantage of allowing precise targeting of defined mutations in a gene by using homologous recombination. (18)
Retrovirus-meditated gene transfer
This method is used to increase to probability of the expression being expressed in the organism; the gene transfer is mediated by means of a carrier or a vector, most commonly a virus or a plasmid. Retroviruses are generally used as vectors to transmit genetic material in to a cell. (18)
The offspring produced using this method are chimerical (i.e. not all cells carry the retrovirus). The only way to transmit the transgene is if it is also bonded to some of the organisms' germ cells. (18)
For all three methods mentioned above the success rate in terms of live birth of the organism which carries the transgene is tremendously low, provided that the transgene does not lead to abortion. The outcome of these experiment rests solely on the first generation (F1) exhibiting the characteristics of the transgene. The F1 generation may produce only chimeras. When this happens the scientists will inbreed the chimeras for ten to twenty generation until homozygous transgenic organisms are acquired. Once a homozygous transgenic organism is acquired its embryos can be frozen and stored for later implantation.
What are moral concerns with Transgenesis?
This article focuses mainly on the benefits, what it is and how it works. However, there are many questions regarding this topic which might go against some ones moral beliefs, such as:
Should there be a standardised protocol for these scientists? (15)
Are human interests the only concern? What about the wellbeing of other living organisms? (15)
Are these scientist "playing god"?
Will Transgenesis affect evolution? (15)
Transgenesis manipulates organisms to increase their production yield and quality for example increased production and quality of milk in cows as well increased pest resistance in crops." Are these valid reasons?
To help answer some of these questions, a survey was done is the small community of Henley on klip, the results of the questionnaire (appendix 4) are as shown in appendix 5 and 6.
Transgenic Questionnaire results