公共英语PETS－2精品阅读31_公共英语

    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.
    克隆实验开始于20世纪50年代,对象为青蛙和蟾蜍。直到1997年,家才成功地克隆了哺乳类动物,即世界闻名的“多莉羊”。克隆技术从那时起得到了持续的进展,今天已有了克隆老鼠、克隆鲑鱼和克隆牛。