To screen for a specific gene replacement when introducing a transgene into animal cells, the cells are screened for:
◦ resistance to G418 and presence of TK activity.
◦ loss of resistance to G418 and loss of TK activity.
◦ resistance to G418 and loss of TK activity.
◦ loss of resistance to G418 and presence of TK activity.
◦ β-galactosidase activity.