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
考研
Nearly a century ago, biologists found that if they separated an invertebrate animal embryo into two parts at an early stage of
Nearly a century ago, biologists found that if they separated an invertebrate animal embryo into two parts at an early stage of
admin
2012-01-05
30
问题
Nearly a century ago, biologists found that if they separated an invertebrate animal embryo into two parts at an early stage of its life, it would survive and develop as two normal embryos. This led them to believe that the ceils in the early embryo are undetermined in the sense that each cell has the potential to develop in a variety of different ways. Late biologists found that the situation was not so simple. It matters in which plane the embryo is cut. If it is cut in a plane different from the one used by the early investigators, it will not form two whole embryos.
A debate arose over what exactly was happening. Which embryo cells are determined, just when do they become irreversible committed to their fates and what are the "morphogenetic determinants" that tell a cell what to become? But the debate could not be resolved because no one was able to ask the crucial questions in a form in which they could be pursued productively. Recent discoveries in molecular biology, however, have opened up prospects for a resolution of the determinants in early development. They have been able to show that, in a sense, ceil determination begins even before an egg is fertilized.
Studying sea urchins, biologist Paul Gross found that an unfertilized egg contains substances that function as morphogenetic determinants. They are located in the cytoplasm of the egg cell, i. e. , in that part of the cell’s protoplasm that lies outside of the nucleus. In the unfertilized egg, the substances ate inactive and are not distributed homogeneously. When the egg is fertilized, the substances become active and, presumable, govern the behavior of the genes they interact with. Since the substances are unevenly distributed in the egg, when the fertilized egg divides, the resulting cells are different from the start and so can be qualitatively different in their own gene activity.
The substances that Gross studied are maternal messenger RNA’s—products of certain of the maternal genes. He and other biologists studying a wide variety of organisms have found that these particular RNA’s direct, in large part, the synthesis of histones a class of proteins that bind to round them to form a structure that resembles beads, or knots, on a string. The beads are DNA segments wrapped around the histone; the string is the intervening DNA. And it is the structure of these beaded DNA strings that guides the fate of the cells in which they are located.
Choose the most appropriate from the four choices to complete the sentence or answer the question.
The passage is most probably directed at which kind of audience?
选项
A、State legislators deciding about funding levels for a state-funded biological laboratory.
B、Readers of an alumni newsletter published by the college that Paul Gross attended
C、Marine biologists studying the processes that give rise to new species.
D、Undergraduate biology majors in molecular biology course
答案
C
解析
转载请注明原文地址:https://jikaoti.com/ti/XtwUFFFM
本试题收录于:
翻译硕士(翻译硕士英语)题库专业硕士分类
0
翻译硕士(翻译硕士英语)
专业硕士
相关试题推荐
rawmaterials
TheculturalandreligiouscrisisthroughwhichtheRomanEmpirewaspassinginthefourthcenturyisoneofthemostsignifican
ThemostfamousnationalepicinOldEnglishliteratureis().
Theeighteenth-centuryBritishthinkerEdmundBurkemadethefollowingobservationaboutthebenefitsofopposition:"Hethatwr
Readthepassagebelowandthendotheexercisesthatfollow.IfaMeccaexistsfortoday’syouth,itmusttaketheformofa
Readthepassagebelowandthendotheexercisesthatfollow.IfaMeccaexistsfortoday’syouth,itmusttaketheformofa
Inadditiontourgetoconformwhichwegenerateourselves,thereistheexternalpressureofthevariousformalandinformalgr
InSaudiArabia,amonarchywhereconservativeIslamprevailsandnomodifiedsystemoflawexists,women’smobilityisstrongly
______ghostexistsintheworld.That’syourillusion.
Youwon’tdieofunhappiness.Contrarytothelong-heldandwidespreadbeliefthatthemorestressedandoutofcontrolyouare
随机试题
导致社会方言产生的原因有()
可用于治疗血流动力学稳定的室性心动过速的药物是
脊柱侧凸手术可能包括的并发症有
感冒风寒束表证的代表方是
已知某企业存货为18万元,流动负债为30万元,速动比率为1.5,假设该企业的流动资产由速动资产和存货构成,则该企业的流动比率为()。
根据所给资料,回答问题。下列城市中,2012年出口额占进出口总额的比重最大的是:
宁某是一家水泥厂的负责人,其于2009年8月与建材经销商安某签订了一份合同,合同中约定,安某由宁某的工厂购入水泥5000吨,分5次交付,每次交付1000吨,每吨800元,总价款400万元,并约定于宁某交付最后一批货物之前安某付清余款。合同订立后,安某向宁某
山西某县根据当地地处高寒山区的实际,大规模实施退耕还林,改善了当地生态环境,增加了农民收入,促进了该县经济的发展。该县的这一做法()。
改革开放以来,我国成功地走出了一条中国特色社会主义的新道路,社会主义在中国也显示出了蓬勃生机,社会主义现代化建设也取得了举世瞩目的巨大成就。但在这一新的历史起点上,坚持和发展中国特色社会主义,仍然要“强调总依据”,根本原因在于
Julietisnotatwork.Sheistakinga_____untiltheendofthisweek.
最新回复
(
0
)