背景大鏈接

Cloning is the asexual production of an exact copy of an original. So for example， one could use cloning to produce the exact copy of a single cell. The cell copy would be identical to the first cell and would have the same exact DNA sequence. In many cases， cloning has been used to reproduce type specific cells. In some instances， cloning of an individual organism， like the sheep， Dolly， has been possible.

Unlike reproduction that involves two “parents，” such as a male and female plants， cloning has a single parent. This is often used in reproducing certain plants. Certain plants have undergone cloning processes for thousands of years， but they do not play a part in the ethical debates that surround cloning of animals， and most particularly humans.

For example， reproductive cloning of animals was first attempted in the 1950s. Most identify the sheep Dolly， cloned in 1996. Dollys parent had DNA transferred into an egg that had its nucleus removed. This is called a somatic cell nuclear transfer. The cell was then treated with chemicals and stimulated to grow so than an almost exact replicate of the cloned sheep was born.

克隆就是通過(guò)無(wú)性繁殖，對(duì)原體的精確復(fù)制。舉例來(lái)說(shuō)，細(xì)胞就可以被完全復(fù)制。生成的細(xì)胞與原細(xì)胞一模一樣，甚至基因鏈也相同。普通實(shí)驗(yàn)都是克隆特型細(xì)胞。當(dāng)然，克隆羊多莉的成功表明有機(jī)體的克隆也是可行的。

有些植物分雌雄，其后代有父有母，而克隆產(chǎn)物不同于此，只有一個(gè)父源。有很多植物也是單性繁殖，數(shù)千年如此而不會(huì)有倫理問(wèn)題。但一旦涉及動(dòng)物甚或人類(lèi)，倫理問(wèn)題便凸顯了。

有例可證，動(dòng)物克隆的嘗試始于20世紀(jì)50年代，多莉則克隆成功于1996年。將其父源基因移植到一去核卵子得以實(shí)現(xiàn)，這一技術(shù)稱(chēng)作體細(xì)胞核移植。改細(xì)胞隨之采用多種化學(xué)物質(zhì)進(jìn)行培育，最終得到了對(duì)其父源完全克隆的多莉。