问题 单项选择题

Ames试验常选用的指示生物为

A.鼠伤寒沙门菌的野生型菌株
B.鼠伤寒沙门菌的组氨酸突变型菌株
C.鼠伤寒沙门菌的色氨酸突变型菌株
D.大肠杆菌的野生型菌株
E.大肠杆菌的色氨酸突变型菌株

答案

参考答案:B

解析: 鼠伤寒沙门菌突变试验是应用最广泛的检测基因突变的方法,是由 Ames于1979年建立,常称Ames试验。利用突变体的测试菌株,观察受试物能否纠正或补偿突变体所携带的突变改变,判断其致突变性。其选用的菌株可以是鼠伤寒沙门菌或大肠杆菌,但最常用的菌株是鼠伤寒沙门菌的组氨酸突变型菌株。

单项选择题
单项选择题

It was a fixing sight: there, in the Capitol itself, a U.S. Senator often mocked for his halting, inarticulate speaking, reached deep into his Midwestern roots and spoke eloquently, even poetically, about who he was and what he believed, stunning politicians and journalists alike.

I refer, of course, to Senator Jefferson Smith. In Frank Capra’s classic Mr. Smith Goes to Washington, Jimmy Stewart plays this simple, idealistic small-town American, mocked and scorned by the big-moneyed, oh-so-sophisticated power elite--only to triumph over a corrupt Establishment with his rock-solid goodness.

At root, it is this role that soon-to-be-ex-Senator Bob Dole most aspires to play: the self effacing, quietly powerful small-town man from Main Street who outwits the cosmopolitan, slick-talking snob from the fleshpots. And why not There is, after all, no more enduring American icon.

How enduring Before Americans had a Constitution, Thomas Jefferson was arguing that the new nation’s future would depend on a base of agrarian yeomen free from the vices inherent in big cities. In 1840 one of the classic, image-driven presidential campaigns featured William Henry Harrison as the embodiment of rural virtues, the candidate of the log cabin and hard cider, defeating the incumbent Martin Van Buren, who was accused of dandified dress and manners.

There is, of course, a huge disconnect between this professed love of the simple, unspoiled life and the way Americans actually live. As a people, Americans have spent the better part of the 20th century deserting the farms and the small towns for the cities and the suburbs; and are torn between vacationing in Disney World and Las Vegas.

U.S. politicians too haven’t exactly shunned the temptations of the cosmopolitan life. The town of Russell, Kansas, often seems to be Dole’s running mate, but the candidate spends his leisure time in a luxury condominium in Bal Harbor, Florida. Bill Clinton still believes in a place called Hope, but the spiffy, celebrity-dense resorts of Martha’s Vineyard and Jackson Hole are where he kicks back. Ronald Reagan embodied the faith-and-family pieties of the front porch and Main Street, but he fled Iowa for a career and a life in Hollywood.

Still, the hunger for the way Americans believe they are supposed to live is p, and the distrust of the intellectual hustler with his airs and his high-flown language runs deep. It makes sense for the Dole campaign to make this a contest between Dole as the laconic, quiet man whose words can be trusted and Bill Clinton as the traveling salesman with a line of smooth patter but a suitcase full of damaged goods. It makes sense for Dole to make his campaign song Thank God I’m a Country Boy--even if he is humming it 9,200 m up in a corporate jet on his way to a Florida condo.

It seems that the author is most critical of some politicians’()

A. hypocrisy

B. elegance

C. prestige

D. absurdity