Embryonic stem cell- mediated gene transfer

- This method involves:
- isolation of stem cells that can develop into any type specialized cell, also known as totipotent cell, from embryos.
- the desired gene is inserted into these cells.
- cells containing the desired DNA are incorporated into the host's embryo, resulting in chimeric animal.

* unlike the other 2 methods, which require live transgenic offspring to test for the presence of the desired transgene, this method allows testing for transgenes at the cell stage.