首页
登录
职称英语
One reason why a sheep, a less well-understood experimental subject
One reason why a sheep, a less well-understood experimental subject
游客
2024-01-11
17
管理
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.
Line 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. [br] Which of the following hypothetical scientific discoveries, if made, would weaken the author’s arguments concerning the ethical risks of human cloning?
选项
A、Through careful and documented study, cloning proves to be less risky than consanguineous breeding.
B、A laboratory process for reducing the number of stages in the cell division process is developed.
C、A non-cloning method for curing human fertility is discovered, thereby reducing the need to rely upon cloning.
D、A procedure for easing the acclimation of a foreign nucleus in the embryonic host is established.
E、A means of assessing genetic mistakes in a foreign nucleus before its implementation into a clone is devised.
答案
E
解析
转载请注明原文地址:https://tihaiku.com/zcyy/3353355.html
相关试题推荐
Theprimarypurposeofthepassageisto______[br]Inresponsetoexperimental
Charlie’sChainsawCompanyhasreasontobelievethatoneofitsmodelsofsawi
Anexperimentalmicrowaveclothesdryerheatsneitherairnorcloth.Rather,it
Inthe1960’s,long-termstudiesofprimatebehavioroftenusedassubjectstama
Researchershavequestionedtheuseofcostlyandexperimentaldiagnostictestt
UnlikethelivesofPushkin,Gogol,Tolstoi,andDodtoevski,subjectsofotherT
Jay:Ofcoursetherearemanygoodreasonstosupporttheexpansionofpreventiv
Claim:Noactisdonepurelyforthebenefitofothers.Reason:Allactions—even
Collegestudentsshouldbeencouragedtopursuesubjectsthatinterestthemrath
Performingrotememoryexercisesrarelyimprovesthe______ofanygivensubject
随机试题
Ingeneral,oursocietyisbecomingoneofgiantenterprisesdirectedbyab
书籍到了我的手里,我的习惯是先看序文,次看目录。页数不多的往往立刻通读,篇幅大的,只把正文任择一二章节略加翻阅,就插在书架上。除小说外,我少有全体读完的
中国特有的山水审美观以及它的外化成果——山水诗、山水散文、山水画、山水园林诞生于
A提示仅受重力作用的静止流体的等压面是水平面。
A. B. C. D.
边缘性骨髓炎好发于() A.上颌骨体部 B.下颌升支 C.上、
根据《药品经营质量管理规范实施细则》,下列关于药品零售叙述正确的是A、药品零售均
A.脑内去甲肾上腺素(NA)升高B.尿中CA无变化C.红细胞钠泵活性无变化D.脑
患者,女性,51岁。身高155cm,体重75kg,因消化性溃疡少量出血入院检查。
在城市给水排水管道工程不开槽法施工方法中,浅埋暗挖法施工适用性强,适用于各种土层
最新回复
(
0
)