What are genetically modified (GM) animals?
How are GM animals created?
Which animals are used?
Why are GM animals useful?
What are the potential hazards associated with GM animals?
Is it ethical?
   
   
What are genetically modified (GM) animals?
 

They are animals that have had changes made to their DNA through molecular techniques. Changes in the DNA give these animals new characteristics.

Transgenic animals are genetically modified animals which have had genes from another species inserted into their DNA. The first GM animals were transgenic mice, created in 1980.  

Since this time, further techniques have been developed. As well as inserting genes, it is now possible to ‘knock out’ specific genes, or to make larger-scale genetic alterations. Such animals are now generally referred to as GM animals.
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How are GM animals created?

The most common method for producing GM animals is to inject the foreign gene into fertilised eggs through a process known as ‘microinjection’.

For mammals, the injected eggs are placed into a ‘foster’ mother where they develop to term. If the foreign gene has been successfully incorporated into the egg’s original DNA, the resultant offspring will carry the extra, foreign DNA.

When this GM animal mates and produces offspring, the foreign gene is inherited in the same way as normal DNA. In this way, scientists can breed a line of GM animals that carries the extra DNA.

A diagrammatic representation of the technique is provided in Diagram 2 below.
Click here for an enlarged diagram.

 
Diagram 2: How to create a transgenic animal
(Graphics by Jeffery Lim, Copyright @ 2007 Singapore Press Holdings. All rights reserved.)
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Which animals are used?
 

The first GM animal, a GM mouse, was made in the early 1980s and this technology has been successfully applied to other animals such as cattle, pigs, sheep, poultry, fish, as well as the insects such as the fruit fly (Drosophila melanogaster).

However, GM mice are still most common - they make up 98% of all GM animals.
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Why are GM animals useful?
 

1. Medical Applications
 

Animal models of human diseases
 

Currently, this is the main medical application for GM animals.

Animals may be genetically engineered to develop human diseases. For example, mice with cystic fibrosis or human cancers have been produced. By studying such animal models, scientists may gain new understandings and insights, leading to the discovery of new treatments and new drugs.
   
 

Determine gene functions

 

Humans and certain animals such as the mice share a high degree of genetic similarity. Thus, the study of genes in GM animals may reveal how similar genes in humans work.

Such use of GM animals is likely to increase significantly, because by modifying a gene, its various roles in different functional systems of the body can be identified.
   
 

Pharming’ for production of therapeutic proteins
 

Farm animals can be genetically modified to produce large quantities of useful substances for treating human patients. They become, in effect,walking pharmacies.

For example, animals such as cows and goats can be genetically engineered to secrete medically valuable proteins into their milk. More recently, a group of British scientists developed GM chickens that are capable of laying eggs containing anti-cancer proteins.
   
 

Xenotransplants (transplantation from another species into humans)

 

Scientists have developed "Knockout pigs" by removing the specific gene that causes pig organs to be rejected by a human body.

This open the possibility of farming pigs for their organs in very much the same way that they are now farmed for pork. This can potentially alleviate the shortage of organs for organ transplants.

   
   
 

2. Agriculture
 

Currently, more than thirty-five varieties of GM fish have been developed around the world.

 

Some GM fish are being developed to grow faster, resist disease, and tolerate different temperatures. At least one company, Aqua Bounty Farms, is currently requesting approval from the U.S. Food and Drug Administration to market its GM salmon for food. Aqua Bounty Farms' GM salmons can grow to more than three times larger than normal salmons within the first year of growth.
   
 

Besides improving fish farm productivity, scientists have also engineered tilapia which can produce human blood clotting factors. There is potential that we can harvest these clotting factors for the treatment of human blood disorders
   
   
 

3. Aesthetic Purposes
 

Associate Professor Gong Zhiyuan of the National University of Singapore has genetically engineered zebrafish that fluoresce due to the expression of jellyfish and anemone genes. Trademarked Glofish, these are the world’s first GM pets and are available in countries such as the United States
   
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What are the potential hazards associated with GM animals?
  Possible hazards of developing GM animals include:
   
 
novel or increased allergic reactions and toxic effects if they are eaten,
changes in behaviour of the GM animals such as increased aggression,
changes in the ability of the GM animal to act as a human disease reservoir,
impact on the ecosystem if the GM animals escaped or are released into the environment.
   
 

The likelihood of these happening is generally considered to be relatively low but certainly should not be neglected.
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Is it ethical?
 

For some, genetic modification of animals is unethical because they feel that it is a form of disrespect to animals or is a violation of animal rights.

However, many others believe that an acceptable balance exists between the need to minimize animal suffering and the need to maximize gain to medicine, agriculture, and scientific understanding. Traditional breeding is also a form of genetic manipulation.
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