Gene Targetting Using Embryonic Stem (ES) Cells - In this technique, embryo derived stem cells are cultured. These seem cells are transfected with a vector containing the desirable gene. This allows targeting of gene to a particular site by homologous recombination.

The rare targeted cells are isolated, multiplied and used for injection of expanded blastocysts, which are then implanted into surrogate mothers to allow the development to be completed. The developed animals can be checked for transgenesis. The different steps of this technique are illustrated.