Topics 7.5.1 and 7.5.2 Application and implications of genetic engineering

                                                 Application and implications of genetic engineering


              Genetically engineered fish carry and transmit one or more copies of recombinant DNA sequence. The genetically engineered fish are also called as transgenic fish. The word recombinant means new combinations of genetic material.

              Genetic engineering is also called as gene technology. It is possible to transfer the selected genes from strong organism to weak organism of the same species or different species in order to get the best traits possible. Some of the traits we, as producers or consumers, expect the faster growth, high food to protein conversion ratio, considerable disease resistance etc.

             Genetic engineering is manipulating the DNA in vitro in a predictable way. The word In vitro means In vitro fertilization (IVF). In-vitro means outside the body. The word fertilization means union of male gamete with female gamete. In-vitro fertilization is carried out in a laboratory dish or in test tube.


It is vital to select the DNA donor. Selection of best donor is done by different ways such as

  1. Stress test: The selected donor group of fish are introduced the stress conditions by changing the various physical and chemical properties of the water, such as temperature, pH, salinity, light etc. The fish or fishes which show the reaction to the stress conditions are selected.
  2. Chemical test: In this method the fish (donor) are treated with some chemicals. The fish which show least reaction are selected.

           After selection of the donor the desired trait causing section in the DNA should be identified from the carefully extracted cell.

           The section of DNA is extracted using the Restriction enzymes. This extracted DNA is introduced into the DNA isolated from another species of fish. The DNA of the donor and the acceptor are merged using the DNA ligase (enzyme).

          The fish with this recombinant DNA show the desired trait.

Important terms:

Gene:  A section of DNA coding for a specific protein
Restriction endonuclease: An enzyme that cuts DNA at a specific base sequence, e.g.
                                                        GAATTC. Each time the sequence occurs, it cuts the DNA. If it
                                                         occurs 5 times, there will be 5 cuts making 6 DNA fragments
Ligase: An enzyme that joins DNA sections
Vector: Something that transfers a gene from one cell to another, usually a
                  bacterial plasmid or a virus
Plasmid: A small circular piece of DNA found in bacteria; it is not part of the
                    main bacterial DNA
Sticky ends: Non-parallel ends of a DNA molecule formed when a restriction
                    enzyme cuts the DNA. They allow other DNA to bond more easily
                    than non-sticky ends.

Flow chart: Insulin producing transgenic bacteria.



Advantages of genetic engineering:

  1. Growth rate of the transgenic fish is fast.
  2. Food to body protein conversion ratio is high.
  3. High adaptability to the new conditions.
  4. High disease resistance etc.

Disadvantages of genetic engineering:

  1. If escaped from captivity the transgenic fish out-compete wild fish.
  2. There will be considerable damage to food chains and food webs.
  3. Modified gene may spread to wild population when there is interbreed between transgenic fish and wild population, which may leads to unforeseen effects on successive generations.
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