Gene Targeting
Transgenes mostly integrate randomly (105)
Special circumstances required for targeting
Positive selection for targeting event
- neomycin resistance gene (G418) included as transferred DNA
- may even be activated by fusion event resulting from x-over
Negative selection for random events
- HSV-TK gene included at either end of linear recDNA
- gancyclovir converted to toxin by HSV-TK
- therefore TK genes must be absent for cells to survive