Transgenic Animal

A transgenic animal is one whose genome has been changed to carry genes from another species or to use techniques for animal genome editing for specific traits. 

Animal features can be changed by purposefully altering the gene. A mouse was the first successful transgenic animal. 

Methods

For the production of transgenic animals three principal methods are applicable: DNA micro-injection, embryonic stem cell-mediated gene transfer and retrovirus-mediated gene. 

1. DNA microinjection: In this process a direct microinjection of a chosen gene takes place from another member of the same species or from a different species into the pro-nucleus of a fertilized ovum. The insertion of DNa is a random process. There is a high probability that the introduced gene will not insert itself into a site on the host DNA that will permit its expression. Then the manipulated fertilized ovum is transferred into the oviduct of a recipient female for further development. 
2. Embryonic stem cell-mediated gene Transfer: This method involves with the prior insertion of the desired DNA sequence by homologous recombination into an in-vitro culture of embryonic stem cells. These stem cells are undifferentiated that have the potential to differentiate into any type of cell (somatic and germ cells) and are capable to give rise to a complete organism. These cells are then incorporated into an embryo at the blastocyst stage of development. The result is a chimeric animal. In this method a choice for gene inactivation takes place and important for genetic control in developmental processes.
3. Retrovirus-Mediated Gene Transfer: A Retroviruses or a plasmid is used as a vector or carrier to increase the probability of expression of gene transfer. Chimeric mice are derived from this method. Transmission of the transgene is possible only if the retrovirus integrates into some of the germ cells.