Vectorless Gene Transfer

Gene transfer can be effected by certain means that do not use vectors. These include

a. Electroporation: Temporary holes are formed in the plasma membrane of the host cell by applying a high voltage. These pores permit entry of foreign DNA.

b. Chemical mediated genetic transformation some chemicals, such as polyethylene glycol, help foreign DNA to enter the host cell.

c. Micro-injection: The host cell is immobilized by applying a mild suction with a blunt pipette. The foreign gene is then injected with a micro-injection needle.

fig. 25.3 Introduction of Foreign DNA in a Host Cell with a Microinjection Needle

d. Particle gun: Tungsten particles coated with foreign DNA are bombarded into the host cell.

Applications of Recombinant DNA Technology

1. To understand molecular events in biological processes such as cell differentiation and aging.

2. It can be used to make precise gene maps.

3. Useful chemical compounds can be produced example: injectable hepatitis B vaccine.

4. It has provided a broad range of tools to aid physicians in the diagnosis of diseases.

Example:

a. Identification of food poisoning by Salmonella,

b. Hepatitis virus

c. HIV

5. Testing the DNA of parents who are carriers for genetic disorders can be done and other chances of producing an afflicted child can be predicted.

Gene Therapy

It means to replace a faulty gene by a normal healthy functional gene.

Example:

Severe Combined Immuno Deficiency (SCID). This disease is caused by a defect in the gene for the enzyme adenosine deaminase (ADA). So in gene therapy, lymphocytes are extracted from the bone marrow of a SCID sufferer. A good copy of the human gene encoding this enzyme is introduced into these cells. This equips these cells with a good copy of the gene, in addition to the existing faulty copy. The cells thus treated are then re-injected to the patients bone marrow.

Lymphocytes now produced have a fully functional ADA gene and they produce ADA to help the patients immune system.