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
One reason why a sheep, a less well-understood experimental subject than the laboratory mouse, should have proved easier
One reason why a sheep, a less well-understood experimental subject than the laboratory mouse, should have proved easier
admin
2009-05-19
49
问题
One reason why a sheep, a less well-understood experimental subject than
the laboratory mouse, should have proved easier to clone may stem from
differences in the initial stages of the two species’ embryonic development.
After reaching maturity in the ovary of the mother, the unfertilized eggs of all
(5) mammals accumulate a supply of proteins, and the means of producing fresh
protein. In this way, the mammalian egg brings with it a larder for the embryo
to make use of until its own genes activate and supply this requirement
themselves. The sheep embryo disposes of its store properly and need not
depend on its own genes until the sixteen-cell stage, four cell divisions
(10) successive to fertilization, while in contrast, the mouse embryo commences this
process more precociously, becoming reliant on the activity of its own genes
after just the first division when the fertilized egg becomes two cells.
Therefore, a foreign nucleus introduced into a sheep egg exploits a respite in its
host’s biological development, allowing it to adapt to its new role before
(15) assuming genetic control.
Concomitantly, a nucleus introduced into a mouse egg must acclimatize
quickly for its genes to be able to direct embryonic development within a single
cell division, so perhaps there is insufficient time for the extensive re-
programming of compulsory gene activity. The human embryo is thought to rely
(20) on its own genes after three cellular divisions, which might or might not
provide time enough for a foreign nucleus to acclimate. However, were
scientists to comprehend the nature of the indispensable re-programming then
there is every likelihood that both mice and humans could be cloned.
Despite the long-standing availability of this technology, there has until
(25) recently been little interest in it. Some people suffering from infertility as a
result of rare hereditary diseases could produce offspring, but cloned individuals
may be at risk given scientists’ limited knowledge of the long term effects of
allowing an "old" adult cell nucleus to commence life again in an egg. The
nucleus of a skin cell could have accumulated a multitude of genetic mistakes of
(30) no consequence to its role in the skin, but the same cell could prove deleterious
in other tissues, or immensely increase the probability of the affliction with
cancer. The threat to general human health posed by cloning, as opposed to the
individual, is difficult to determine, but the risks are almost certainly lower
than those encountered in the effective inbreeding of consanguine marriages,
(35) and thus there are no scientific grounds per se for banning cloning. Like other
practices inconsequential to the physical well being of humanity, but generally
deemed undesirable on moral or social grounds, the prohibition of human
cloning will ultimately rest with only a simple pragmatic decision.
选项
A、advancing an argument against human cloning based on evidence from cloning experiments performed on lower life forms
B、measuring the technical and ethical limitations of the embryonic cloning process in mammals
C、refuting arguments against human cloning through the use of hard scientific evidence
D、illuminating the critical ethical distinctions in process between human cloning and sheep cloning
E、describing how the ethical issues in the quest for human cloning have given rise to new models of embryonic development
答案
B
解析
转载请注明原文地址:https://jikaoti.com/ti/2FdYFFFM
本试题收录于:
GRE VERBAL题库GRE分类
0
GRE VERBAL
GRE
相关试题推荐
Whatisthepurposeofthepassage?Whatcanweinferfromthepassage?
DeathValleyisoneofthemostfamousdesertsintheUnitedStates,coveringawideareawithitsalkalisand.Almost20percen
Youmusthavebeentroubledbywhentosay"Iloveyou"becauseitisoneofthegreatestpuzzlesinourlife.Whatifyous
Itwasanearlymorninginsummer.Inthestreets,sleepyeyedpeopleweremovingquickly,headingtowardstheirjobs.Thiswas
LincolnthoughtitwaswrongtokeepNegroes______slaves.
Therewasonethoughtthatairpollutionaffectedonlytheareaimmediatelyaroundlargecitieswithfactoriesandheavyautomob
Therewasonethoughtthatairpollutionaffectedonlytheareaimmediatelyaroundlargecitieswithfactoriesandheavyautomob
Thegrowthofachildisinfluencedbyanumberoffactors,______arebeyondourcontrol.
Ourschool-runfactory______variouskindsofchemicaldeviceslastyear.
DAMPEN:ENTHUSIASM::
随机试题
通过谈话、讨论、参观、访问对学生进行德育的方法属于()。
治夜盲,眼目昏涩,可选用的药物是()
男婴,孕34周早产,无窒息。出生后4小时开始出现呼吸困难,呈进行性加重。听诊双肺呼吸音减弱,未闻及干、湿啰音。胸部X线片示双肺野弥漫性毛玻璃样改变。该患婴的初步诊断为
图示时序逻辑电路为()。附:触发器的逻辑状态表为:
在卫生部、国家环保总局于2003年10月10日发布的《医疗废物分类名录》中,危险废物的分类包括()。
专制型教师对学生的态度会使学生形成下列哪一种人格特点()
对做出突出成绩的文职人员的奖励不包括()。
某单位为业务技能大赛获奖职工发放奖金,一、二、三等奖每人奖金分别为800、700和500元。11名获一、二、三等奖的职工共获奖金6700元,问有多少人获得三等奖?
教科书的编写要同时兼顾学科知识的逻辑顺序和受教育者学习的——。
Properarrangementofclassroomspaceisimportanttoencouraginginteraction.Mostofushavenoticedhowimportantphysicalse
最新回复
(
0
)