-Transgenic animals are animals that develop from a fertilized egg with a foreign gene insert carry that gene in every cell.Transgene is the foreign gene.-

For transgenesis, DNA can be introduced into mice by one of the following methods ;

-Retroviral vectors that infects the cells of an early stage embryo prior to implantation into a receptive female.

-Microinjection into the enlarged sperm nucleus (the male pronucleus) of a fertilized egg

-Introduction of genetically engineered embryonic stem cells into an early stage developing embryo prior to implantation into a receptive female.

-Transfer of diploid somatic nuclei into an enucleated oocyte .

microinjection of DNA is currently the preferred method for producing transgenic mice .

1-the gene of interest is usually a cloned recombinant DNA molecule .

2-this gene could be micro injected into early mouse embryo (fertilized egg) which contain two pronuclei , one from the sperm (male) and one from the egg (female)

3 -a few hundred copies of the foreign DNA in about 2 picoliters of solutions are microinjected directly into one of the pronuclei.

4 -the injected embryos are then transferred to the oviduct of a foster mother, and upon subsequent implantation in the uterus.

--The number that have the foreign DNA integrated into their chromosomes is between a few percent and 40 percent.

- the introduced DNA appears to integrate randomly without preference for a particular chromosome location.

•The production of transgenic animals by microinjection of DNA into fertilized eggs.

5 -three weeks after the birth ,the offspring are checked for the presence of the transgene by southern blotting of DNA extracted from a small piece of the tail.

-Screening can be performed rapidly using the polymerase chain reaction (PCR) if suitable primers are available.

1-Analysis of DNA regulatory elements. 2-Expression of proteins during

differentiation. 3-Potential role of oncogene products on

growth, differentiation and induction of tumorigenesis.

4-Transgenic mice can be used to model human disease .the aim is to ultimately replace defect gene in developing embryo (gene therapy)

.In fact , transgenic animal model hold promise for future methodologies to correct genetic diseases early in fetal development.