新视野大学英语 读写教程第三册 unit8-c

　　Section (C)
Twins Six Years Apart
Scientists in Scotland recently announced that, for the first time, they have cloned an exact copy ofan adult mammal. The cloned lamb, named Dolly, has the exact same genes¹ as the adult sheep fromwhich she was cloned. In other words, the two are identical twins; only Dolly is six years younger. Thegoal of the Scottish scientist Ian Wilmut is to develop a way to raise identical sheep that producemedicines for humans.
A week after Wilmut's announcement, other scientists revealed that they had used a differenttechnique to clone monkeys, which are much more closely related to humans. These accomplishmentsimmediately set off a worldwide debate: Should scientists be allowed to clone animals? Is cloningmorally wrong and dangerous — or is it a valuable research tool?
All attempts at cloning were largely unsuccessful until 1984. That's when a scientist in Denmarkseparated cells from a sheep's embryo² (胚胎). An embryo is an early stage of development in whichcells are busy dividing and "transforming" into specialized³ cells like skin, eye, or muscle cells.
Unlike a skin cell, an embryo is on its way to becoming a complete living thing: The Danish scientistcombined an embryo cell with an egg cell from another sheep. He put the combined cell — then a newlygrowing embryo — into a grown female sheep. To much surprise, the embryo grew into a baby lamb.
Since then, other scientists have used embryos⁴ to clone cattle, pigs, goats, rabbits - and, now, evenmonkeys.
So what makes Wilmut's sheep unique? Instead of using early-stage embryo cells, Wilmut used cellsfrom the udder (乳腺) of an adult sheep. In theory, that's like using one of your skin cells to clone a newyou!
Wilmut knew that each cell of the body contains a full set of genetic⁵ instructions — instructions togrow a complete individual. (The only exceptions are egg and sperm⁶ cells, each of which contains halfthe genes to grow a new individual.) Once cells have specialized, on their way to becoming skin or eyeor udder cells, most of the genetic instructions to make a full being are turned off. Until now, scientistsbelieved that specialized cells could not be used to form a complete living thing.
Wilmut proved them wrong. He found a way to take an udder cell and make it grow into a new clonedlamb. An amazing fact: Dolly has no biological father.
Wilmut's success didn't come easily. He has been studying this problem for more than two decades.
Last year, he used embryos to successfully clone two sheep. Then he went ahead to clone an adultsheep. But, of 277 udder cells he fused with egg cells, only 30 began to develop into embryos. Heimplanted 29 of those into female sheep. Only one adult gave birth to a lamb.
Other scientists have jumped in to repeat Wilmut's experiment with other animals, including cows.
And that's what has scientists, animal-rights advocates, politicians — even President Clinton — up inarms. How far, they wonder, will cloning go?
Wilmut maintains that cloning animals has tremendous potential for helping⁷ people. Cloned sheep, hesays, could be used as living drug factories. Scientists could "engineer" sheep that produce drugs intheir milk. And by altering the proteins on the surfaces of animal organs to make them more likehuman organs, scientists believe they may be able to create a plentiful⁸ source of organ donors¹⁰ forpeople.
Why not clone humans as organ donors? Theoretically, Wilmut says, there is no reason histechniques couldn't someday be used to clone people. Think about the possibilities: a whole basketballteam of Michael Jordans, a scientific panel of Albert Einsteins, a movie starring and co-starring BradPitts.
On a more serious note, some experts argue that couples who have difficulty having a baby couldmake copies of themselves. And parents whose child has a fatal disease like cancer might be able toclone the child, creating a twin who could be a bone-marrow (骨髓) donor⁹.
But even Ian Wilmut draws the line at cloning humans. "All of us would find that offensive," he says.
Several countries, including Britain, Denmark, Germany, and Australia, have made all scientific work oncloning humans illegal. The U.S. has no such law, but President Clinton has set up a panel of scientistsand philosophers to study the issue. In the meantime, Clinton has imposed a ban on using federalmoney to clone humans.
Humans are more than the sum of their genes, argues a philosopher at one research institute.
Though they look exactly the same, clones are not necessarily exact copies. The younger twin mightgrow up with different influences — say, unusual friends or special teachers. A cloned Albert Einsteinmight fail his physics class. A cloned pop star might sing terribly.
Say you were cloned. Would your twin live a shorter life because he or she started out with DNA¹¹ thatwas already 10, 20, or 30 years old? Scientists aren't sure. And how could you prevent someone fromtaking a sample of your hair and making a clone of you? Again, no solutions.
Some people who oppose cloning also object to the use of animals as research tools. "Next, they'll becloning foxes to make more fur (毛皮) coats," says the president of an animal rights group.
What do you think? Should scientists be allowed to clone animals? How about humans?　　

1 genes   

n.基因( gene的名词复数 )

参考例句：

• You have good genes from your parents, so you should live a long time. 你从父母那儿获得优良的基因，所以能够活得很长。 来自《简明英汉词典》
• Differences will help to reveal the functions of the genes. 它们间的差异将会帮助我们揭开基因多种功能。 来自英汉非文学 - 生命科学 - 生物技术的世纪

2 embryo   

n.胚胎，萌芽的事物

参考例句：

• They are engaging in an embryo research.他们正在进行一项胚胎研究。
• The project was barely in embryo.该计划只是个雏形。

3 specialized   

adj.专门的，专业化的

参考例句：

• There are many specialized agencies in the United Nations.联合国有许多专门机构。
• These tools are very specialized.这些是专用工具。

4 embryos   

n.晶胚；胚，胚胎( embryo的名词复数 )

参考例句：

• Somatic cells of angiosperms enter a regenerative phase and behave like embryos. 被子植物体细胞进入一个生殖阶段，而且其行为象胚。 来自辞典例句
• Evolution can explain why human embryos look like gilled fishes. 进化论能够解释为什么人类的胚胎看起来象除去了内脏的鱼一样。 来自辞典例句

5 genetic   

adj.遗传的，遗传学的

参考例句：

• It's very difficult to treat genetic diseases.遗传性疾病治疗起来很困难。
• Each daughter cell can receive a full complement of the genetic information.每个子细胞可以收到遗传信息的一个完全补偿物。

6 sperm   

n.精子，精液

参考例句：

• Only one sperm fertilises an egg.只有一个精子使卵子受精。
• In human reproduction,one female egg is usually fertilized by one sperm.在人体生殖过程中，一个精子使一个卵子受精。

7 helping   

n.食物的一份&adj.帮助人的，辅助的

参考例句：

• The poor children regularly pony up for a second helping of my hamburger. 那些可怜的孩子们总是要求我把我的汉堡包再给他们一份。
• By doing this, they may at times be helping to restore competition. 这样一来, 他在某些时候,有助于竞争的加强。

8 plentiful   

adj.富裕的，丰富的

参考例句：

• Their family has a plentiful harvest this year.他们家今年又丰收了。
• Rainfall is plentiful in the area.这个地区雨量充足。

9 donor   

n.捐献者；赠送人；(组织、器官等的)供体

参考例句：

• In these cases,the recipient usually takes care of the donor afterwards.在这类情况下，接受捐献者以后通常会照顾捐赠者。
• The Doctor transplanted the donor's heart to Mike's chest cavity.医生将捐赠者的心脏移植进麦克的胸腔。

10 donors   

n.捐赠者( donor的名词复数 )；献血者；捐血者；器官捐献者

参考例句：

• Please email us to be removed from our active list of blood donors. 假如你想把自己的名字从献血联系人名单中删去，请给我们发电子邮件。
• About half this amount comes from individual donors and bequests. 这笔钱大约有一半来自个人捐赠及遗赠。 来自《简明英汉词典》

11 DNA   

(缩)deoxyribonucleic acid 脱氧核糖核酸

参考例句：

• DNA is stored in the nucleus of a cell.脱氧核糖核酸储存于细胞的细胞核里。
• Gene mutations are alterations in the DNA code.基因突变是指DNA密码的改变。