Linearized and purified conditional targeting vector was used to electroporate ES cells. After G418 and Gancyclovir selection, 24 ES drug-resistant colonies were picked out and one of them was confirmed as positive by Southern hybridization. 条件打靶载体线性化和电泳纯化后用于对ES细胞电穿孔,经G418和Gancyclovir双药选择后挑选出抗药性克隆24个,获得一个经Southern杂交鉴定的阳性克隆。