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
97
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
Whatshouldonedoifhewantstoworkmoreefficientlyathislowpointinthemorning?
Itisoftensaidthatthesubjectstaughtinschoolsaretooacademicinorientationandthatitwouldhemoreusefulforchildr
Beforeabigexam,asoundnight’ssleepwilldoyoubetterthanporingovertextbooks.That,atleast,isthefolkwisdom.And
Whatnaturalresourcesdidthesouthernparthave?
WhydoestheWesternmovieespeciallyhavesuchaholdonourimagination?Chiefly,Ithink,becauseitoffersseriousinsights
Aneconomistissomeonewhoknowsalotabouthowgoodsandwealthareproducedandused.Food,for(31)______,isakindofgoo
PaoloFril,chairmanandscientificofficerofGeneDupe,basedinSanMelito,California,isamanwithadream.Thedreamisa
part-time
UNSecretary-GeneralKofiAnnanvisitedthetroubledDarfurregionofwesternSudanThursdaytoconsiderwaystoendthehumanit
Friday本题答案信息也是隐含在最后一个话轮男士的最后一句中:...orjustcomehereonthenextmorningtogettheresult。这一题与上一题的听音和答题紧密相关,因为前面说的是Thursday(星期
随机试题
人眼视近物时主要表现为
完整的内分泌疾病的诊断一般不包括
下列不属于月经后期常见病机的是
基本存款账户的存款人可以通过本账户办理日常转账结算和现金缴存,但不能办理现金支取。()
学过长方形的面积计算公式后,再学习正方形的面积计算公式。这种学习属于()。
I______myclothes,andthephonerang.
温家宝总理在给一位国务院参事的回信中,引用了两句诗:“知屋漏者在宇下,知政失者在草野。”这一古训蕴含的哲理是()。
通常,人们会认为只有剧烈的运动才能够燃烧脂肪,可是研究表明,经常爬楼梯也是一个可以消耗脂肪的运动,同时也是锻炼心血管功能的有效辅助练习。研究称,一个体重超重的人在一年内能够每天坚持爬两层楼梯,那么他有望减掉十二公斤的体重。以下选项如果为真,最不支持上述观点
二次型f(x1,x2,x3)=(x1+x2)2+(x2+x3)2-(x3-x1)2的正惯性指数与负惯性指数依次为()
Amace-wieldingclownlashesatabearcub.Anelephantstandsonitsrearlegsonthepointofastungun,electricarcsrunnin
最新回复
(
0
)