Transgenesis is the process of introducing a gene (known as a transgene) from one organism into the genome of another organism. The aim is that the resulting transgenic organism will express the gene and have some new property or characteristic. This is made possible by the fact that the genetic code is universal for all living things. Examples are the transfer of human genes into animals or cultured cells, especially to produce molecules with therapeutic value, and the transfer of cloned genes to another breed or species.
Transgenic or genetically modified organisms, be they bacteria, viruses or fungi, serve all kinds of research purposes. Transgenic plants, insects, fish and mammals (including Humans) have been bred. Transgenic plants such as corn and soybean have replaced wild strains in agriculture in some countries. Transgene escape has been documented for GMO crops since 2001 with persistence and invasiveness.
Steps for Transgenesis
A gene that codes for a desirable trait or protein must first be identified. Researchers may identify desirable traits in other species and try to identify the gene responsible. There are many techniques that can be used to identify the gene sequence that codes for the specific protein / trait of interest. If the protein has been isolated it may be possible to determine its amino acid sequence (or part thereof). If the amino acid sequence is known it may be possible to determine part of the gene sequence using a codon table, however there will usually be several different possible sequences due to the redundancy of the genetic code. Once a small part of the sequence has been determined it may be possible to construct a DNA probe that will stick the target gene. Other techniques that may be used to identify a gene include:
- Gene Chips (Microarrays)
- DNA Sequencing
The target gene must then be isolated. DNA from the organism that contains the target gene can usually be isolated simply by breaking up cells mechanically or with chemical treatments such as detergents. The DNA can be separated from the other cell components using a technique called centrifugation. To separate the target gene from the rest of the DNA it would first be cut using a restriction enzyme. The fragments would then be separated according to size using a technique called Gel Electrophoresis. The fragment that contains the target gene can be identified using a DNA probe and can then be cut out of the gel and amplified (copied) using PCR.
Alternatively the gene could be inserted into a bacterial plasmid using DNA Ligase
The bacteria would then copy the gene each time it underwent cell division (a technique called Gene Cloning.
A vector is then used to transfer the target gene (transgene) into the organism being modified. There are many different vectors / techniques used to transfer the transgene depending on the cell type etc. However, if the gene is inserted on it’s own it is unlikely that it will be expressed. Special promoter and termination sequences might be needed on either side of the gene in order for it to be expressed. The type of promoter might determine where (in which tissues) the protein is expressed. The final DNA sequence that is prepared including the target gene and associated regulatory sequences is called a Gene Construct.