Almost all the work on transgenic animals is still at the research level. The topic is included in the syllabus on account of its inherent interest and the immense potential for future commercial applications.

The intention is only that students acquire, and be able to recall or discuss, as appropriate:

• outline knowledge of one approach currently being applied to farmed animals, as given below (several techniques for producing transgenic animals are in parallel use at the research level; most are conceptually too difficult for consideration here);
  

• some appreciation of the potential for using transgenic animals;
  

• an appreciation of some of the ethical issues raised.

Technique

1. DNA containing the desired gene is identified and cloned.
   
2. Cattle, pigs or sheep are made to superovulate, and their eggs collected. (Technically these are oocytes, but this term will not be expected of students).
   
3. The eggs are fertilised in vitro.
   
4. A solution of the DNA is injected into the fertilised eggs using a very fine hollow glass needle, the process being monitored microscopically. Some of the fertilised eggs take up the DNA which becomes incorporated into a chromosome.
   
5. The embryos are cultured in vitro for a time, then implanted into surrogate mothers to complete their development.

Potential benefits

(Students will not be required to recall all of these examples. Other valid examples will be acceptable.)

Potential applications being pursued include transfer to cattle andor other animals of genes for:

1. Disease resistance.
   
2. Abnormally high quantities of growth hormone, to increase meat production.
   
3. Proteins of medical importance to humans. (This encompasses a vast array of substances and has already been achieved in some instances, for example transgenic sheep which secrete human blood clotting factor IX in their milk exist in research stations).
   
4. Production of milk low in cholesterol.
   
5. Increased ability to digest cellulose.
   
6. The polled (hornless) condition in cattle.

There is also exciting potential for correction of genetic disorders in humans (gene therapy).

Background

Another rapidly-moving field is the potential use of transgenic pigs for use as organ transplant donors to humans. One commercial company has, by injecting human genes into pig embryos, produced a herd of genetically modified pigs. The objective is to make available donor organs which, because they display human proteins, will engender a much reduced response by the human immune system and hence will be far less liable to suffer rejection. The first such transplant from pig to human was expected during 1996.

A stimulus to this research is the decreasing availability of human donors in the face of a hugely increasing demand. Very substantial financial benefits could be expected to accrue to companies successful in this area, particularly as patients will need very long term drug therapy after transplantation.

Interest in this field has been further quickened by recent successes achieved in the cloning of sheep. (An article on cloning of farmed animals will appear on the Gene Web). A combination of gene transfer, followed by cloning, could yield a vast source of potential transplant material.

There is, however, deep concern over the possibility that viruses may be transferred from donor animals, in which they have no obvious effects, to humans, where they may show virulence. If this occurs, the consequences for human health could be devastating. The risk is not quantifiable.

Ethical problems

There are many, students will readily suggest some. The dilemmas are not readily resolvable and are likely to continue to place a brake on this research. The points which might be considered include:

1. the extent to which animals may suffer and to what extent, if at all, any such suffering may be justifiable.
   

2. should animals deliberately be modelled to develop human diseases, such as cystic fibrosis or cancer?
   

3. the presently very error-prone nature of the techniques involved.
   

4. the possibility of transmitting potentially very virulent pathogens (see previous Background box).