Microinjection for transgenic animals is a direct method to introduce DNA into either cytoplasm or nucleus. DNA microinjection methods are used to transfer the genes between animals. This is quite a popular technique for creating transgenic organisms. DNA microinjection is also known as the pronuclear microinjection. In this process, the genes must be transmitted through the germ line, including germ cells of the animal that contains the same modified genetic material. Transgenic animals are those consequences of experimental application, wherein the DNA integrated in their germ line. The first transgenic animals were produced in the year of 1980. Mice were one of the first transgenic animals at that time.
Transgenic animals are used to identify the functions of specific factors in homeostatic systems through the over- or under-expression of a modified gene. Transgenic animals are useful for disease models and producers of substances for humans. Some transgenic animals are produced for specific economic features. As for example, the transgenic cattle were created to produce more milk containing particulars for human proteins, which may be of help in the treatment of the human body. The embryonic stem cell-mediated gene transfer system is the method involves the prior insertion of the desired DNA sequence by homologous recombination into an in vitro culture of embryonic stem cells.
The importance of these cells as vectors for genetic modification of the organism is based upon the discovery of Smithies that in tissue culture, donor gene constructs can replace these corresponding segments of host DNA by homologous recombination. Although it is not possible that the escape of transgenic animals will not genetically contaminate wild animal populations, and these concerns are probably not serious.
Laboratory animal strains are far less capable of surviving in the wild than are their feral counterparts. It is highly unusual for foreign genes to confer a selective advantage upon transgenic animals. Under most circumstances, new genes are neutral with respect to animal health or are deleterious. So, for the most part, transgenic animals are especially dependent upon the laboratory environment for survival.
Now, let us discuss the different aspects of the advantages and disadvantages of such transgenic animals.
Advantages:
For Industry: such as goats that produce spider silk for materials production.
In Agriculture: such as larger sheep that grow more wool.
In Medicine: such as cows that produce insulin in their milk.
Disadvantages:
There may be a high mortality rate and other deleterious effects on animals used by researchers to create transgenic breeds. This is been observed that most of the transgenic pigs are having an enhanced growth rate and an efficient feed conversion ratio that exhibits reduced reproductive performance and may be subject to suffer from arthritis and dermatitis etc.
The transgenic animal project is extremely expensive.
The generation of transgenic animals is also expensive, because of long gestation period, litter size and higher maintenance cost of the recipient animals.