21世纪大学英语读写教程第一册10

Unit 10

Text A

Listening

First Listening
Before listening to the tape, have a quick look at the following words and phrases.

overseas
向海外

fantasy
幻想

cell
细胞

gene
基因

identical twins
同卵双生胎

Second Listening
Listen to the tape again. Then, choose the best answer to each of the following questions.

1. The main purpose of this listening passage is _________.
A) to give information about a new scientific discovery
B) to discuss political problems in the United States
C) to argue for cloning
D) to argue against cloning
2. Which of the following is the best definition of the verb "to clone"?
A) to be re-elected president for a second term
B) to photocopy an entire book
C) to make a genetic copy of an animal or a person
D) to transplant an organ from an animal to a human
3. According to the listening, cloning humans is _________.
A) not yet possible
B) highly controversial
C) illegal in the United States
D) both A) and B)
4. The listening concludes that most questions about cloning _________.
A) will be decided by the courts
B) are up to each individual concerned
C) have not yet been answered
D) do not really matter

Cloning:
good Science or Baaaad Jdea

Chana Freimans Stiefel

Just before President Clinton heads to the hospital for knee surgery, he asks another Bill Clinton to meet Russian President Boris Yeltsin at an overseas meeting. Meanwhile, a third Bill Clinton is out playing golf, while a fourth is helping daughter Chelsea with a science project.
Sound far-fetched? That day may come. Scientists in Scotland recently announced that, for the first time, they have cloned an exact copy of an adult sheep. The cloned baby lamb, named Dolly, has the exact same genes as the adult sheep from which she was cloned. In other words, the two are identical twins; only Dolly is six years younger. The goal of embryologist lan Wilmut, the lead scientist, is to develop a way to raise identical sheep that produce medications for humans.
A week after Wilmut's announcement, scientists in Oregon disclosed that they had used a different technique to clone monkeys, close cousins of humans. Faster than you can say "Frankenstein," these accomplishments triggered a worldwide debate: Should scientists be allowed to clone animals? Will humans be next? Is cloning unethical and dangerous—or is it a valuable research tool?
All attempts at cloning were largely unsuccessful until 1984. That's when a scientist in Denmark separated cells from a sheep's embryo. An embryo is an early stage of development in which cells are busy dividing and "transforming" into specialized 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 scientist combined an embryo cell with an egg cell from another sheep. He implanted the fused cell - then a newly growing embryo - into a grown female sheep. To much surprise, the embryo grew into a baby lamb. Since then, other scientists have used embryos to clone cattle, pigs, goats, rabbits - and, now, even monkeys.
So what makes Wilmut's sheep unique? Instead of using early-stage embryo cells, Wilmut used cells from the udder of an adult sheep. In theory, that's like using one of your skin cells to clone a new you!
Wilmut knew that each cell of the body contains a full set of genetic instructions—a blueprint to grow a complete individual. (The only exceptions are egg and sperm cells, each of which contains half the genes to grow a new individual.) Once cells have specialized, on their way to becoming skin or eye or udder cells, most of the genetic instructions to make a full being are turned off. Until now, scientists believed that specialized cells could not be used to form a complete organism.
Wilmut proved them wrong. He found a way to "reprogram" an udder cell and make it grow into a new cloned lamb. An amazing fact: Dolly has no biological father.
Wilmut's success didn't come easily. He has been studying reproductive science for more than two decades. Last year, he used embryos to successfully clone two sheep. Then he forged ahead to clone an adult sheep. But, of 277 udder cells he fused with egg cells, only 30 began to develop into embryos. He implanted 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 activists, politicians—even President Clinton — up in arms. How far, they wonder, will cloning go?
Wilmut maintains that cloning animals has tremendous potential for helping people. Cloned sheep, he says, could be used as living drug factories. Scientists could "engineer" sheep that produce drugs in their milk. And by altering the proteins on the surfaces of animal organs to make them more like human organs, scientists believe they may be able to create a plentiful source of organ donors for people.
Why not clone humans as organ donors? Theoretically, Wilmut says, there is no reason his techniques couldn't someday be used to clone people. Think about the possibilities: a whole team of Michael Jordans, a scientific panel of Albert Einsteins, a movie starring and co-starring Brad Pitt.
On a more serious note, some fertility specialists argue that couples who have difficulty conceiving a baby could make copies of themselves. And parents whose child has a fatal disease like cancer might be able to clone the child, creating a twin who is an exact match for bone-marrow donation.
But even lan 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 outlawed all scientific work on cloning humans. The U.S. has no such law, but President Clinton has set up a panel of scientists and ethicists to study the issue. In the meantime, Clinton has imposed a ban on using Federal money to clone humans.
Humans are more than the sum of their genes, argues Mark Hanson, an ethicist at an ethics research institute in Briarcliff Manor, New York. Though they look exactly the same, clones are not necessarily carbon copies. The younger twin might grow up with different influences—say, unusual friends or special teachers. A cloned Albert Einstein might flunk physics. A cloned Madonna might sing off-key.
Say you were cloned. Would your twin live a shorter life because he or she started out with teenage genes? Scientists aren't sure. And how could you prevent someone from taking a sample of your hair and making a clone of you? Again, no solutions.
Some opponents of cloning also object to the use of animals as research tools. "Next, they'll be cloning minks and foxes to make more fur coats," says Cleveland Amory, president and founder of the Fund for Animals, an animal rights group.
What do you think? Should scientists be allowed to clone animals? How about humans?
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