Have you ever wished you could have a clone of yourself to do your homework while you went out to play with your friends? Imagine if you could really do that, where would you start?

　　What exactly is cloning?

　　Cloning is a way of making an organism (有机体) that is an exact genetic (基因的) copy of another. This means that every single bit of DNA is the same between the two!

　　You might not believe it, but there are human clones among us right now. They weren't made in a lab, though. They're identical (同样的) twins, created naturally. Below, we'll see how natural identical twins relate to modern cloning technologies.

　　How is cloning done?

　　You may have first heard of cloning when Dolly the sheep showed up on the scene in 1997. Cloning technologies have been around for much longer than Dolly, though.

　　How does one go about making an exact genetic copy of an organism? There are a couple of ways to do this：artificial embryo twinning (人工胚胎双生) and somatic cell nuclear transfer (体细胞核移植). How do these processes differ?

　　1．Artificial Embryo Twinning

　　Artificial embryo twinning is the relatively low­tech version of cloning. As the name suggests, this technology mimics the natural process of creating identical twins.

　　2．Somatic Cell Nuclear Transfer

　　Somatic cell nuclear transfer (SCNT), uses an approach different from artificial embryo twinning, but it produces the same result: an exact clone，or a genetic copy, of another. This was the method used to create Dolly the sheep.

　　Section_ⅠWarming Up & Reading - Pre­reading

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　　CLONING：WHERE IS IT LEADING US?

　　Cloning has always been with us and is here to stay. It is a way of making an exact① copy of② another animal or plant. It happens in plants when gardeners take cuttings③ from growing plants to make new ones. It also happens in animals when twins④ identical⑤ in sex and appearance are produced from the same original egg. The fact is that these are both examples of natural clones⑥. 　　①exact/Iɡ'zækt/adj.精确的；准确的

　　②make a copy of (＝copy)复制

　　of making ...作way的定语。

　　③cutting/'kʌtIŋ/n.剪枝；剪报；剪纸

　　④twin/twIn/n.双胞胎之一；孪生儿之一 adj.成对的；成双的

⑤identical/aI'dentIkl/adj.同一的；一模一样的

　　⑥The fact is that ...中，that引导表语从句。