Transgenic animal
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Transgenic animals are animals produced with externally introduced genes. Transgenic animals can be used in many fields and as models to test the effect of certain genes on health. They can be used to produce "enhanced" versions of an animal.
They can also be used as bioreactors: animals that produce an extra substance we want. Imagine having a transgenic cow that is modified to produce insulin in large quantities in its milk. This insulin can then be purified from the cows milk and used in replacement therapy for treating patients with diabetes mellitus.
How do transgenic animals contribute to human welfare? The benefits of these animals to human welfare can be grouped into areas:
* Agriculture * Medicine * Industry
The examples below are not intended to be complete but only to provide a sampling of the benefits.
1. Agricultural Applications
a) breeding Farmers have always used selective breeding to produce animals that exhibit desired traits (e.g., increased milk production, high growth rate).11,15,17 Traditional breeding is a time-consuming, difficult task. When technology using molecular biology was developed, it became possible to develop traits in animals in a shorter time and with more precision. In addition, it offers the farmer an easy way to increase yields.
b) quality Transgenic cows exist that produce more milk or milk with less lactose or cholesterol12, pigs and cattle that have more meat on them8,17, and sheep that grow more wool18. In the past, farmers used growth hormones to spur the development of animals but this technique was problematic, especially since residue of the hormones remained in the animal product.
c) disease resistance Scientists are attempting to produce disease-resistant animals, such as influenza-resistant pigs, but a very limited number of genes are currently known to be responsible for resistance to diseases in farm animals.19
2. Medical Applications
a) xenotransplantation Patients die every year for lack of a replacement heart, liver, or kidney. For example, about 5,000 organs are needed each year in the United Kingdom alone.25 Transgenic pigs may provide the transplant organs needed to alleviate the shortfall.9 Currently, xenotransplantation is hampered by a pig protein that can cause donor rejection but research is underway to remove the pig protein and replace it with a human protein.25
b) nutritional supplements and pharmaceuticals Products such as insulin, growth hormone, and blood anti-clotting factors may soon be or have already been obtained from the milk of transgenic cows, sheep, or goats.3,12,23 Research is also underway to manufacture milk through transgenesis for treatment of debilitating diseases such as phenylketonuria (PKU), hereditary emphysema, and cystic fibrosis.3,13,23,25
In 1997, the first transgenic cow, Rosie, produced human protein-enriched milk at 2.4 grams per litre. This transgenic milk is a more nutritionally balanced product than natural bovine milk and could be given to babies or the elderly with special nutritional or digestive needs.4,21,23 Rosie's milk contains the human gene alpha-lactalbumin
c) human gene therapy Human gene therapy involves adding a normal copy of a gene (transgene) to the genome of a person carrying defective copies of the gene. The potential for treatments for the 5,000 named genetic diseases is huge and transgenic animals could play a role. For example, the A. I. Virtanen Institute in Finland produced a calf with a gene that makes the substance that promotes the growth of red cells in humans.24
3. Industrial Applications
In 2001, two scientists at Nexia Biotechnologies in Canada spliced spider genes into the cells of lactating goats. The goats began to manufacture silk along with their milk and secrete tiny silk strands from their body by the bucketful. By extracting polymer strands from the milk and weaving them into thread, the scientists can create a light, tough, flexible material that could be used in such applications as military uniforms, medical microsutures, and tennis racket strings.1
Toxicity-sensitive transgenic animals have been produced for chemical safety testing. Microorganisms have been engineered to produce a wide variety of proteins, which in turn can produce enzymes that can speed up industrial chemical reactions.
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