下一步是证明胚胎干细胞对生殖系有贡献。Embryos from one mouse strain were injected with ES cells from another mouse strain. These mosaic embryos (i.e. composed of cells from both strains) were then carried to term by surrogate mothers. The mosaic offspring was subsequently mated, and the presence of ES cell-derived genes detected in the pups. These genes would now be inherited according to Mendel�s laws.
埃文斯现在开始对胚胎干细胞进行基因改造,为此选择了将基因整合到染色体中的逆转录病毒。他演示了这种逆转录病毒DNA从胚胎干细胞通过花叶小鼠转移到小鼠生殖系。埃文斯用胚胎干细胞培育出携带新遗传物质的小鼠。
卡佩基改进了针对基因的策略,并开发了一种可以普遍应用的新方法(正-负选择)。
基因靶向帮助我们了解了数百个基因在哺乳动物胎儿发育中的作用。capecchi的工作揭示了几种人类先天畸形的原因。埃文斯应用基因靶向技术开发了人类疾病的小鼠模型。年代mithies also used gene targeting to develop mouse models for inherited diseases such as cystic fibrosis and the blood disease thalassemia. He has also developed numerous mouse models for common human diseases such as hypertension and atherosclerosis.