In genetic engineering, the methods of gene transfer lead to the production of transgenic animals and plants. These are called genetically modified organisms. Transgenism has been recognized as one of the thrust areas of biotechnology.
The uptake of genes by the cells in animals is called trans fection. The transfected cells are used for a variety of purposes such as 1. The production of chemicals and pharmaceutical drugs, 2. Study of structure and function of genes and 3. Production of transgenic animals of commercial value such as livestock animals and fishes. It is also called molecular farming. In transfection, fertilized eggs/embryos or the cultured cells are employed.
The transfection of fertilized egg involves either the transfer of whole nuclei or whole chromosomes; or their fragments or the DNA segments.
A. For the transfer of whole nuclei, the cells are treated with cytochalasin B and enucleated. The enucleated cells are incubated with the desired karyoplasts (nuclei) for induction in presence of polyethylene glycol (PEG).
B.For transfer of whole chromosomes, metaphase cells are subjected to hypotonic lysis and individual chromosomes or fragments are isolated and then incubated with whole cells/eggs for transfection.
C. Microinjection of DNA segments : In this the fertilized eggs are injected with DNA segments for integration. DNA integrated eggs are then used for getting transgenic animals.
D. Transfer of genes to cultured cells : In this stem cells are used. The stem cells are undifferentiated precursor cells. In these cultured cells, the gene can be delivered through vectors like retroviruses or directly by techniques such as microinjection using particle gun, electroporation or by the use of liposomes.
Transgenic animals have been produced in a variety of animals such as mice, rabbits, sheeps, pigs, goats, cows, fishes etc.
1. Transgenic animals are more efficient than their normal counterpart in feed assimilation.
2. They exhibit faster growth and hence achieve the marketable size sooner.
3.Meat quality is good.
4.They are resistant to certain diseases.
5. They serve as bioreactors for obtaining valuable recombinant proteins and pharmaceuticals from their milk or urine or blood.