Genetically Modified Birds

Fig. 3: Gene therapy using an Adenovirus vector. Source: Wikipedia (2009). 
 
1.3.2 Gene Deletion 
This is the removal of an unwanted and undesired gene from an organism. Here, the restriction enzyme e.g. 
endonuclease, is used to cut off the undesired gene. The sticky ends of the newly modified gene are allowed to 
overlap with the vector and the new recombinant DNA is delivered to the host cell. 
1.3.3. Gene Regulation/Termination 
This is used when we don‟t want to delete the gene. Here, an antisense messenger RNA (mRNA) of the gene is 
synthesized and introduced into the cell, during protein synthesis, a sense mRNA is produced by the cell and 
this combines with the antisense mRNA and protein synthesis is inhibited. Antisense molecule is a molecule 
which binds specifically to a (sense) strand of RNA or to a DNA helix and stops it being used to code for a 
protein. Antisense molecules are usually chemical derivatives of DNA or RNA. 
1.4. Cases Where Genetic Engineering Has Been Applied Successfully 
The first biotechnology product approved for human health care was the synthetic human insulin which came 
onto the market in the United States in 1982. Since then, more than 170 biotechnology related drugs and 
vaccines have been approved by the United States Food and Drug Administration, of which 113 are currently on 
the market. Another 350 biotechnology medicines, together targeting over 200 diseases, are in the later stages of 
development. Amongst those approved during 2000 are medicines to treat pneumococcal diseases in children, 
diabetes, cancer and haemophilia [2]. Genetic engineering has also been used in gene therapy. Gene therapy 
involves the genetic engineering of a patient‟s genetic code to remove or replace a mutant gene that is causing 
disease. There are two broad types of gene therapy that are possible. Germ line, or stem-cell, gene therapy 
involves altering patients' DNA in their stem (reproductive) cells. The modification to their genetic “blueprint” 
is permanent, and hereditary. This type of gene therapy is complex, and is considered too risky to undertake 
until the underlying biology is better understood. It also raises many ethical concerns, for example, over the 
potential misuse of the therapy to create “designer” babies. At the moment, germ-line gene therapy is banned in 
many countries. The second type of therapy is somatic gene therapy. This involves engineering cells on a 
“localized” basis, without affecting the patient‟s basic genetic “blueprint”. The first such therapy was approved 
in 1990 to treat a four-year-old child suffering from severe combined immune deficiency (SCID). Some of the 
child‟s white blood cells were extracted, genetically engineered in the laboratory and infused back into her 
bloodstream. This successfully strengthened her immune system. Gene therapy techniques for cystic fibrosis 
have also been approved, and candidate techniques for the treatment of Parkinson‟s disease, Alzheimer‟s disease 
and some cancers are under development. Somatic gene therapy is likely to become very important for the 
treatment of diseases caused by single mutant genes [2].