首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Dolly was once an awfully lonely sheep. When the famous cloned (of an exact copy of a plant or animal made by taking a cell from
Dolly was once an awfully lonely sheep. When the famous cloned (of an exact copy of a plant or animal made by taking a cell from
admin
2009-03-21
105
问题
Dolly was once an awfully lonely sheep. When the famous cloned (of an exact copy of a plant or animal made by taking a cell from it and developing it artificially) animal made headlinesin 1997, she was the only mammal ever to be manufactured from the cell of an adult donor. Since then, the clone ranks have swelled, with mice and cattle also making their way out of the labs. Last week cloning technology took another step forward when an international biotechnology company announced that it had created a litter of five genetically identical piglets (young pigs), and that it had a pretty good idea of how they could one day be used as organ donors for ailing humans.
The idea of turning pigs into
tissue factories
has been around for at least 30 years. Pigs breed easily and mature quickly, and their organs are roughly the same size.as those of humans, meaning operations can be performed with a relative snap-out, snap-in simplicity. The problem is, once the donor organ is stitched in place, the body rebels, rejecting it even more violently than it would a human transplant. " A pig heart transplanted in a person would turn black within minutes, " says David Ayares, a research director with PPL Therapeutics, the biotech firm that helped clone Dolly and also produced the piglets.
What causes pig organs to be rejected so quickly is a sugar molecule on the surface of pig cells that identifies the tissue as unmistakably nonhuman. When the immune system spots this marker, it calls out its defenses. PPL scientists recently succeeded in finding the gene responsible for the sugar and knocking it out of the nucleus of a pig cell. Their next step would be to extract that nucleus, insert it into a pig ovum, and then into the womb of a host pig. The sugar free piglet that was eventually born could then be cloned over and over as a source of safe transplant organs. The idea is to arrive at the ideal animal and repeatedly copy it exactly as it is. The cloned piglets PPL introduced to the world last week were created in just this way, though for this first experiment in pig replication the scientists left the sugar genes intact.
Despite this recent success, PPL is not likely to be setting up its organ shop anytime soon. Knocking out the key sugar gene solves only the problem of short-term rejection. Much more has to be done before any solution to long-term rejection can be found. Nonetheless, Ayares is optimistic, insisting that pig organs could be available in as little as five years. For the present, even a little new transplant material is a big improvement over what’s available, and for gravely ill patients awaiting a donor, that’s no small thing.
The "tissue factories" in the second paragraph most probably refers to
选项
A、the five genetically identical piglets.
B、places for the production of tissues.
C、animals whose organs would be used for human consumption.
D、animals which would be raised in quantity for transplant materials.
答案
D
解析
从文中第一段最后一句与第二段前两句话可以看出tissue factories指的是专门用来大量培养移植器官的动物体,故正确答案为D选项。
转载请注明原文地址:https://kaotiyun.com/show/B8Pd777K
本试题收录于:
公共英语四级笔试题库公共英语(PETS)分类
0
公共英语四级笔试
公共英语(PETS)
相关试题推荐
Themanbehindthisnotion,JackMaple,isadandywhoaffectsdarkglasses,homburgs(翘边帽)andtwo-toeshoes;yethehasbecomes
"Themoregadgetsthereare,the【31】______thingsseemtoget."saidHonoreErvin,co-authorofTheEtiquetteGirls:ThingsYou
A=WashingtonD.C.B=NewYorkCityC=ChicagoD=LosAngelesWhichcity...istheheadquarteroftheSupremeCourt?
Beforeabigexam,asoundnight’ssleepwilldoyoubetterthanporingovertextbooks.That,atleast,isthefolkwisdom.And
Allinternationalchainschoolsteachmanydifferentlanguages.
Note:AnswereachquestionbychoosingA,B,CorDandmarkitonANSWERSHEET1.Somechoicesmayberequiredmorethanonce.
Earthquakescanbedevastating【1】disasters.TheinfamousSanFranciscoearthquakeof1906causedover$200millionworthofdam
AnswerQuestions71to80byreferringtothefollowingfourarticlesconcerningmentalillness.Answereachquestionbychoosin
Itisoftensaidthatthesubjectstaughtinschoolsaretooacademicinorientationandthatitwouldbemoreusefulforchildr
Artwasherfavoritesubjectatschool,butshedidadegreeingeography.
随机试题
固定式龙门铣床水平铣头在立柱上垂直移动(W轴线)对垂直铣头移动(Y轴线)的垂直度超差时如何调整?
关于胸大肌的位置、起止和作用的叙述正确的是【】
术前常规禁食的主要目的是
医师在执业活动中除正当治疗外,不得使用
由于架子工把脚手板铺得太差而加以修正的时间属于()。
( )是指股票的市场价格反映影响股票价格信息的充分程度。
《本草纲目拾遗》中记叙了“强水”,写道:“性最烈,能蚀五金……其水甚强,五金八石皆能穿滴,惟玻璃可盛。”这里的“强水”是指()。
“给定资料”结尾写道:“我们或许应该如作家米兰.昆德拉所言,要“慢下来’,因为自在有为的生活是急不得的。”请结合你对这句话的思考,联系自己的感受和社会实际,自拟题目,写一篇文章。要求:(1)自选角度,见解深刻;(2)参考“给定
下列著名宫殿与所在国家对应不正确的是()。
在社会主义社会个人收入实行按劳分配的原则,是马克思主义的一项基本原理。对这一原理的基本内涵理解正确的是()。
最新回复
(
0
)