问题 单项选择题

下列关于染色体变异的叙述,正确的是()

A.染色体增加某一片段可提高基因表达水平,是有利变异

B.染色体缺失有利于隐性基因表达,可提高个体的生存能力

C.染色体易位不改变基因数量,对个体性状不会产生影响

D.通过诱导多倍体的方法可克服远缘杂交不育,培育出作物新类型

答案

参考答案:D

解析:

染色体片段的增加、缺失和易位等结构变异,会使排列在染色体上的基因数目和排列顺序发生改变,C错误;大多数染色体结构变异对生物体是不利的,有的甚至会导致生物体死亡,A、B错误;远缘杂交得到的F1是不育的,通过诱导使其染色体数目加倍进而可育,由此可以培育作物新类型,D正确。

多项选择题
单项选择题

LAST month, America’s National Law Journal told its readers that "employment lawyers are warning lovestruck co-workers to take precautions in the office before locking lips outside". The advice came too late for Harry Stonecipher. The boss of Boeing was forced to resign last weekend—for reasons that will strike many outsiders as absurd—after his board were told of an affair that the 68-year-old married man had been conducting with a female employee "who did not report directly to him".

Inevitably, as the week rolled on, details of the affair rolled out. The other party was reported to be Debra Peabody, who is unmarried and has worked for Boeing for 25 years. The couple were said to have first got together at Boeing’s annual retreat at Palm Desert, California in January. After that much of the affair must have been conducted from a distance: Mr. Stonecipher’s office is at Boeing’s headquarters in Chicago; Ms Peabody runs the firm’s government-relations office in Washington, DC. They exchanged e-mails, it seems, as office lovers tend to do these days, and therein probably lay Mr Stonecipher’s downfall.

Lewis Platt, Boeing’s chairman, said that Mr Stonecipher broke a company rule that says: "Employees will not engage in conduct or activity that may raise questions as to the company’s honesty, impartiality, reputation or otherwise cause embarrassment to the company." Having an affair with a fellow employee is not, of itself, against company rules; causing embarrassment to Boeing is. It seems that the board judged that the contents of the lovers’ e-mails would have been bad for Boeing had they been made public. Gone are the days when a board considered such matters none of its business, as Citibank’s did in 1991 when its boss, John Reed, became the talk of Wall Street for having an affair with a stewardess on Citi’s corporate jet.

At Boeing, a whistleblower is said to have forwarded the messages to Mr Platt. In general, e-mails are encrypted and not accessible to anyone who does not know the sender’s password. But many firms install software designed to search electronic communications for key words such as, "sex" and "CEO". A study last year of 840 American firms by the American Management Association found that 60% of them check external e-mails (incoming and outgoing), while 27% scrutinize internal messages between employees. Sweet nothings whispered by the water cooler may travel less far these days than electronic billets doux.

Boeing is particularly sensitive to embarrassment at the moment. Mr. Stonecipher was recalled from retirement only 15 months ago, after the company’s previous boss, Phil Condit, and its chief financial officer, Michael Sears, had left in the wake of a scandal involving an illegal job offer to a Pentagon official.

Mr Stonecipher, a crusty former number two at Boeing, was brought back specifically to raise the company’s ethical standards and to help it be seen in its main (and affectedly puritanical) market, in Washington, DC, as squeaky clean. Verbally explicit extra-marital affairs are inconsistent with such a strategy, it seems, though they are not yet enough to bring down future kings of England.

In corporate life, such affairs are hardly unusual. One survey found that one-quarter of all long-term relationships start at work; another found that over 40% of executives say they have been involved in an affair with a colleague, and that in half of these cases one or other party was married at the time. Many a boss has married his assistant and lived happily ever after. Boeing apparently used to accept this: Mr. Condit’s fourth wife was a colleague before they married.

Which of the following is true according to the text()

A. Mr Stonecipher had worked for Boeing for only 15 months when he resigned

B. The previous boss of Boeing also had an office affair before he was fired

C. Boeing company makes great efforts to maintain its ethical standards

D. Extra-marital affairs are not acceptable in most American corporations