新视野大学英语读写教程听力 第三册 te-unit08-c
日期:2012-05-06
[by:恒星英语学习网|//www.julie-photo.com|恒星英语||恒星英语学习网]
[00:00.00]喜欢hxen.com，就把hxen.com复制到QQ个人资料中！Twins Six Years Apart
[00:04.00]1 Scientists in Scotland recently announced that,
[00:09.36]for the first time,
[00:10.94]they have cloned an exact copy of an adult mammal.
[00:15.88]The cloned lamb, named Dolly,
[00:19.69]has the exact same genes as the adult sheep from which she was cloned.
[00:25.63]In other words, the two are identical twins;
[00:32.18]only Dolly is six years younger.
[00:35.60]The goal of the Scottish scientist Ian Wilmut
[00:40.68]is to develop a way to raise identical sheep
[00:44.35]that produce medicines for humans.
[00:47.77]2 A week after Wilmut's announcement,
[00:52.13]other scientists revealed
[00:53.82]that they had used a different technique to clone monkeys,
[00:58.79]Which are much more closely related to humans.
[01:02.39]These accomplishments immediately set off a worldwide debate:
[01:09.26]Should scientists be allowed to clone animals?
[01:14.92]Is cloning morally wrong and dangerous —
[01:20.10]or is it a valuable research tool?
[01:23.12]3 All attempts at cloning were largely unsuccessful until 1984.
[01:30.22]That's when a scientist in Denmark separated cells from a sheep's embryo.
[01:37.20]An embryo is an early stage of development
[01:42.17]in which cells are busy dividing
[01:45.12]and "transforming" into specialized cells like skin, eye, or muscle cells.
[01:53.29]4 Unlike a skin cell, an embryo is on its way to becoming a complete
[01:59.56]living thing:
[02:01.03]The Danish scientist combined an embryo cell with egg cell from another sheep.
[02:08.88]He put the combined cell — then a newly growing embryo
[02:14.42] — into a grown female sheep.
[02:17.23]To much surprise, the embryo grew into a baby lamb.
[02:23.50]Since then, other scientists have used embryos to clone
[02:30.08]cattle, pigs, goats, rabbits — and, now, even monkeys.
[02:36.46]5 So what makes Wilmut's sheep unique?
[02:41.71]Instead of using early-stage embryo cells,
[02:46.90]Wilmut used cells from the udder of an adult sheep.
[02:52.15]In theory, that's like using one of your skin cells to clone a new you!
[03:00.65]6 Wilmut knew that each cell of the body
[03:04.82]contains a full set of genetic instructions —
[03:08.39]instructions to grow a complete individual.
[03:12.28](The only exceptions are egg and sperm cells,
[03:17.71]each of which contains half the genes to grow a new individual.)
[03:23.00]Once cells have specialized,
[03:26.78]on their way to becoming skin or eye or udder cells,
[03:31.25]most of the genetic instructions to make a full being are turned off.
[03:37.22]Until now, scientists believed that specialized cells
[03:42.05]could not be used to form a complete living thing.
[03:46.22]7 Wilmut proved them wrong.
[03:50.69]He found a way to take an udder cell and make it grow into a new cloned lamb.
[03:58.07]An amazing fact: Dolly has no biological father.
[04:04.62]8 Wilmut's success didn't come easily.
[04:08.22]He has been studying this problem for more than two decades.
[04:13.69]Last year, he used embryos to successfully clone two sheep.
[04:19.34]Then he went ahead to clone an adult sheep.
[04:23.99]But, of 277 udder cells he fused with egg cells,
[04:30.76]only 30 began to develop into embryos.
[04:35.11]He implanted 29 of those into female sheep.
[04:41.92]Only one adult gave birth to a lamb.
[04:46.63]9 Other scientists have jumped in to repeat
[04:50.88]Wilmut's experiment with other animals,
[04:53.65]including cows. And that's what has scientists,
[04:58.62]animal-rights advocates, politicians —
[05:01.86]even President Clinton — up in arms.
[05:05.93]How far, they wonder, will cloning go?
[05:10.39]10 Wilmut maintains that cloning animals
[05:14.86]has tremendous potential for helping people.
[05:18.71]Cloned sheep, he says, could be used as livng drug factories.
[05:25.26]Scientists could "engineer" sheep that produce drugs in their milk.
[05:30.84]And by altering the proteins on the surfaces of animal organs
[05:35.88]to make them more like human organs,
1/2 1 2 下一页 尾页
[00:00.00]喜欢hxen.com，就把hxen.com复制到QQ个人资料中！Twins Six Years Apart
[00:04.00]1 Scientists in Scotland recently announced that,
[00:09.36]for the first time,
[00:10.94]they have cloned an exact copy of an adult mammal.
[00:15.88]The cloned lamb, named Dolly,
[00:19.69]has the exact same genes as the adult sheep from which she was cloned.
[00:25.63]In other words, the two are identical twins;
[00:32.18]only Dolly is six years younger.
[00:35.60]The goal of the Scottish scientist Ian Wilmut
[00:40.68]is to develop a way to raise identical sheep
[00:44.35]that produce medicines for humans.
[00:47.77]2 A week after Wilmut's announcement,
[00:52.13]other scientists revealed
[00:53.82]that they had used a different technique to clone monkeys,
[00:58.79]Which are much more closely related to humans.
[01:02.39]These accomplishments immediately set off a worldwide debate:
[01:09.26]Should scientists be allowed to clone animals?
[01:14.92]Is cloning morally wrong and dangerous —
[01:20.10]or is it a valuable research tool?
[01:23.12]3 All attempts at cloning were largely unsuccessful until 1984.
[01:30.22]That's when a scientist in Denmark separated cells from a sheep's embryo.
[01:37.20]An embryo is an early stage of development
[01:42.17]in which cells are busy dividing
[01:45.12]and "transforming" into specialized cells like skin, eye, or muscle cells.
[01:53.29]4 Unlike a skin cell, an embryo is on its way to becoming a complete
[01:59.56]living thing:
[02:01.03]The Danish scientist combined an embryo cell with egg cell from another sheep.
[02:08.88]He put the combined cell — then a newly growing embryo
[02:14.42] — into a grown female sheep.
[02:17.23]To much surprise, the embryo grew into a baby lamb.
[02:23.50]Since then, other scientists have used embryos to clone
[02:30.08]cattle, pigs, goats, rabbits — and, now, even monkeys.
[02:36.46]5 So what makes Wilmut's sheep unique?
[02:41.71]Instead of using early-stage embryo cells,
[02:46.90]Wilmut used cells from the udder of an adult sheep.
[02:52.15]In theory, that's like using one of your skin cells to clone a new you!
[03:00.65]6 Wilmut knew that each cell of the body
[03:04.82]contains a full set of genetic instructions —
[03:08.39]instructions to grow a complete individual.
[03:12.28](The only exceptions are egg and sperm cells,
[03:17.71]each of which contains half the genes to grow a new individual.)
[03:23.00]Once cells have specialized,
[03:26.78]on their way to becoming skin or eye or udder cells,
[03:31.25]most of the genetic instructions to make a full being are turned off.
[03:37.22]Until now, scientists believed that specialized cells
[03:42.05]could not be used to form a complete living thing.
[03:46.22]7 Wilmut proved them wrong.
[03:50.69]He found a way to take an udder cell and make it grow into a new cloned lamb.
[03:58.07]An amazing fact: Dolly has no biological father.
[04:04.62]8 Wilmut's success didn't come easily.
[04:08.22]He has been studying this problem for more than two decades.
[04:13.69]Last year, he used embryos to successfully clone two sheep.
[04:19.34]Then he went ahead to clone an adult sheep.
[04:23.99]But, of 277 udder cells he fused with egg cells,
[04:30.76]only 30 began to develop into embryos.
[04:35.11]He implanted 29 of those into female sheep.
[04:41.92]Only one adult gave birth to a lamb.
[04:46.63]9 Other scientists have jumped in to repeat
[04:50.88]Wilmut's experiment with other animals,
[04:53.65]including cows. And that's what has scientists,
[04:58.62]animal-rights advocates, politicians —
[05:01.86]even President Clinton — up in arms.
[05:05.93]How far, they wonder, will cloning go?
[05:10.39]10 Wilmut maintains that cloning animals
[05:14.86]has tremendous potential for helping people.
[05:18.71]Cloned sheep, he says, could be used as livng drug factories.
[05:25.26]Scientists could "engineer" sheep that produce drugs in their milk.
[05:30.84]And by altering the proteins on the surfaces of animal organs
[05:35.88]to make them more like human organs,
1/2 1 2 下一页 尾页