The first cloning experiments in the 1950s involved frogs and toads. It was not until 1997 that scientists successfully cloned the first mammal, the now world-famous sheep known as Dolly. Cloning techniques have continued to improve since then, and today there are cloned mice, salmon, and cattle.
    克隆實(shí)驗(yàn)開(kāi)始于20世紀(jì)50年代，對(duì)象為青蛙和蟾蜍。直到1997年，科學(xué)家才成功地克隆了哺乳類動(dòng)物，即世界聞名的“多莉羊”?？寺〖夹g(shù)從那時(shí)起得到了持續(xù)的進(jìn)展，今天已有了克隆老鼠、克隆鮭魚(yú)和克隆牛。