What are Transgenic Animals?
Trangenic animals are the animals with the modified genome. A foreign gene is inserted into the genome of the animal to alter its DNA. This method is done to improve the genetic traits of the target animal.
Initially, the improvement of genetic traits was done by selective breeding methods. In this, the animals with desired genetic characteristics were mated to produce an individual with improved genetic characteristics. Since this technique was time-consuming and expensive, it was later replaced by recombinant DNA technology.
Transgenesis is the phenomenon in which a foreign gene with desired characteristics is introduced into the genome of the target animal. The foreign gene that is introduced is known as the transgene, and the animal whose genome is altered is known as transgenic. These genes are passed on to the successive generations.
The transgenic animals are genetically engineered and are also known as genetically modified organisms. The first genetically modified organism was engineered in the year 1980.
Examples : Feather less Chicken, Designer Babies,Hypo Allergic Pets, Sudden death Mosquitoes, Super cow, Popeye Pigs / Enviro Pigs, Spider silk, GM sheep, GFP Bunny / GM Rabbit, GM Monkey, GM Dogs, Glowing Kitten, GLO fish / Super fish, GM Goats, GM Mice, Knock out Mouse.
Let us have a detailed look at the process, importance and applications of transgenic animals.
Methods for Creating Transgenic Animals
The transgenic animals are created by the following methods:
Physical Transfection
In this method, the gene of interest is directly injected into the pronucleus of a fertilized ovum. It is the very first method that proved to be effective in mammals. This method was applicable to a wide variety of species. Other methods of physical transfection include particle bombardment, ultrasound and electroporation.
Chemical Transfection
One of the chemical methods of gene transfection includes transformation. In this method, the target DNA is taken up in the presence of calcium phosphate. The DNA and calcium phosphate co-precipitates, which facilitates DNA uptake. The mammalian cells possess the ability to take up foreign DNA from the culture medium.
Retrovirus-Mediated Gene Transfer
To increase the chances of expression, the gene is transferred by means of a vector. Since retroviruses have the ability to infect the host cell, they are used as vectors to transfect the gene of interest into the target genome.
Viral Vectors :
Viruses are used to transfect rDNA into the animal cell. The viruses possess the ability to infect the host cell, express well and replicate efficiently.
Bactofection :
It is the process by which the gene of interest is transferred into the target gene with the help of bacteria.
Examples of Transgenic Animals :
Following are the examples of transgenic animals:
Dolly Sheep :
Dolly the sheep was the first mammal to be cloned from an adult cell. In this, the udder cells from a 6-year-old Finn Dorset white sheep were injected into an unfertilized egg from a Scottish Blackface ewe, which had its nucleus removed. The cell was made to fuse by electrical pulses. After the fusion of the nucleus of the cell with the egg, the resultant embryo was cultured for six to seven days. It was then implanted into another Scottish Blackface ewe which gave birth to the transgenic sheep, Dolly.
Transgenic Mice :
Transgenic mice are developed by injecting DNA into the oocytes or 1-2 celled embryos taken from female mice. After injecting the DNA, the embryo is implanted into the uterus of receptive females.
Applications Of Transgenic Animals :
The transgenic animals are created because of the benefits they provide to the man. Let us discuss a few of them here.
Normal Physiology and Development
In transgenic animals, a foreign gene is introduced due to which the growth factor is altered. Hence, these animals facilitate the study of gene regulation and their effect on the everyday functions of the body.
Study of Diseases
Transgenic animals are specially designed to study the role of genes in the development of certain diseases. Moreover, in order to devise a cure for these diseases, the transgenic animals are used as model organisms. These transgenic models are used in research for the development of medicines. For example, we have transgenic models for diseases such as Alzheimer’s and cancer.
Biological Products
A number of biological products such as medicines and nutritional supplements are obtained from transgenic animals. Research for the manufacture of medicines to treat diseases such as phenylketonuria (PKU) and hereditary emphysema is going on. The first transgenic cow, Rosie (1997), produced milk containing human protein (2.4 grams per litre). This milk contains the human gene alpha-lactalbumin and could be given to babies as an alternative to natural cow milk.
Vaccine Safety
Transgenic animals are used as model organisms for testing the safety of vaccines before they are injected into humans. This was conventionally done on monkeys.
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