单选题某些转座过程中( )是作为一种中间体存在的。

单选题将S型细菌杀死，分别分离纯化出DNA、RNA、蛋白质和多糖荚膜，然后混合起来用______处理后与R型活细菌共同感染小鼠，则不出现转化现象，不能引起肺炎。

单选题假定一个座位上有20个复等位基因，那么可能存在的基因型有______。

单选题That rapscallion who leaps off the monkey bars, landing smack onto an innocent 3-year-old bystander, and skips off, giggling all the while? According to a new paper out of Israel, he may not feel all that bad about the incident. The study, conducted by Dr. In bal Kivenson Bar-On at the University of Haifa, shows that high levels of fearlessness in 3-and 4-year-olds is strongly associated with aggression and a lack of sympathy. This news will likely surprise risk-loving America, where parents typically beam with pride when their undaunted child mounts the big slide. Fearlessness is a far-end point on the spectrum of what psychologists call the "approach and withdrawal dimension"—people's tendency to approach new stimuli (to gain information and acquire new skills ) and withdraw from unfamiliar stimuli (to avoid danger). Striking the right balance is considered crucial to man's survival. But what about preschoolers'? There's a clear downside, Dr. Kivenson Bar-On discovered, after she observed lots of preschool play and machinations. In total, she documented 80 children at preschool, home and in the lab, measuring their propensity for fearlessness and other social and emotional characteristics at the beginning and end of one year. Fearlessness was measured by observing reactions to various fright-inducing situations: separation from parents, the roar of a vacuum cleaner, a jack-in-the-box and the like. Those who displayed greater levels of fearlessness, the study found, had no trouble recognizing facial expressions of anger, surprise, happiness and sadness in other children—but they had a hard time identifying fear. Over all, they were "emotionally shallow" and showed lower levels of sympathy. They took advantage of friends and lacked regret over inappropriate conduct. "These findings," the paper explains, " suggest that fearlessness in preschool constitutes a clear risk factor for developmental pathways that lead to problems in morality, conscience development, and severe antisocial behaviors. " At the same time, fearless children tended to be highly sociable. "One of the most interesting findings was that we could discriminate between friendliness and sympathy," Dr. Kivenson Bar-On said. "These kids are curious, easygoing and friendly, but they have a hard time recognizing emotional distress in others. " Jamie Ostrov, a psychology professor at the State University at Buffalo who studies aggression, says that children at the extreme end of the fearless spectrurn "may be charming, but they're also highly manipulative and deceptive and skilled at getting their way—even at age 3 or 4. " It could be that fearless children need stronger distress cues to active their autonomic nervous systems, limiting their ability to detect distress cues in others. It seems to be, if I'm not worried about this, you can't be, either. But should we be?

单选题"The imperative to self-knowledge has always been at the heart of philosophical inquiry," wrote MIT professor Sherry Turkle in the insightful book about the web and the self, Life on the Screen: Identity in the Age of the Internet. Published in 1995 as the second part of a trilogy that examined our relationships with technology, it looked at how we are who we are in online spaces. And what that means for us offline. The good news is that the results are positive: "Play has always been an important aspect of our individual efforts to build identity," she said, referencing developmental psychologist Erik Erikson, and nodding to the theories of psychoanalysts Freud, Lacan and Jung. "In terms of our views of the self," she wrote, "new images of multiplicity, heterogeneity, flexibility, and fragmentation dominate current thinking about human identity. " At the time Life on the Screen was released, most of the visitors were college students and their professors from a remarkably small talent pool, and a surprisingly small geography. They were tech-savvy, and generically open-minded about the new fields of virtual exploration that lay within the networks of this new communication platform. They were, in other words, liberal, enlightened types who were more willing to embrace the unprecedented fluidity of self-expression that this new technology uniquely afforded. As a psychoanalyst and a web user herself, Turkle spent much of the book explaining why the articulation of multiple personalities wasn't pathological. Contrary to its Latin root, identity need not mean "the same", she argued. "No one aspect can be claimed as the absolute, true self", she wrote, maintaining that the web allowed us the opportunity to get to know our "inner diversity". In the great psychoanalytic tradition, she said that self-actualisation meant coming to terms with who we are, and integrating each aspect of it into a coherent and well-integrated us. Almost everyone has experienced this kind of identity play. Even if you've never ventured into an online game or been a signed-up member of a web community, you've probably developed a profile for a social network, written a blog, styled a website, commented on an article. But things are different from the time when Turkle was writing Life on the Screen. Nowadays, our virtual social lives are increasingly integrated. with our offline social lives. The freedom of expression is curtailed by the threat of offline consequences from online actions. Today, your reputation offline is far more closely tied to your reputation online than before. In fact, our experience of contemporary identity online is disarmingly similar to offline. However, I still subscribe to the old Turkle. Consequence-free online environments allow us to practise and play without fear of offline effect, and offer an extraordinary place to experience the fluidity of our selves: I can be anyone, even a dog. As Tom MacMaster found, there still are places online where this is possible.

单选题When two of the world's richest and mightiest men pledge to destroy an enemy, it is time to pay attention. Bill Gates, the former boss of Microsoft who now devotes all his time to his charitable foundation, travelled this week to New York, the city run by Michael Bloomberg, to join his fellow billionaire's campaign to stamp out smoking. Have the two potentates met their match? Despite decades of work by health campaigners, more than one billion people still smoke today. Smoking kills up to half of those who fail to quit puffing, reducing their lives by an average of 10 to 15 years. The World Health Organisation (WHO) says more than 5 million people a year die early from the effects (direct or indirect) of tobacco. That exceeds the combined toll of HIV/AIDS, tuberculosis and malaria. Despite that dismal situation, there are three reasons to give the latest pair of campaigners a slim chance of success: money, methods and motivation. Messrs Gates and Bloomberg vowed to spend a combined total of $ 500 million on discouraging the weed. Since Mr. Bloomberg's charity had already announced an award of $125 million earlier, the new money pledged this week totalled a "mere" $ 375 million: $ 250 million from the mayor, and a fresh $ 125 million from the software magnate's philanthropic outfit. How will this cash be spent? In quite innovative ways, and that is a second reason for optimism. Hitherto, most anti-smoking funds have been channelled through a few large bureaucracies. But Mr. Bloomberg's charity wants to let a thousand flowers bloom: in other words, to lend a hand to many initiatives, both public and private, to see what works. There will be a competitive grant scheme for poor countries where the tobacco habit is spreading. The very fact that two giants are teaming up is a landmark in American philanthropy- comparable to Warren Buffett's decision, two years ago, to put his fortune at the disposal of Mr. Gates' foundation. As part of their joint commitment, Mr. Gates is giving some of his $ 125 million directly to Mr. Bloomberg's charity; the rest will go to carefully monitored projects in India, China and other places where the number of smokers is rising relentlessly. Then there is motivation. There are other big players in this cause, and that should induce every new entrant to try bringing something fresh to the party. Earlier this year the WHO started a campaign against tobacco known as MPower. One of its selling points was that in contrast with many other projects, it had a fairly clear idea about what was needed. WHO experts have listed a series of tactics, ranging from aggressive public education to a rise in tobacco taxes, that deliver results. (Even if high taxes lead to some smuggling and diversion, studies done in Brazil, for example, show that fiscal measures do curb consumption. ) The World Bank, which funded that research, is also thought to be ready to join the anti-smoking scrum after years of paying little attention. A crowded field, indeed. But having an extra $ 500 million from two hard-driven billionaires surely won't hurt.

单选题入噬菌体侵入大肠杆菌细胞后通过( )而进入溶源状态。

单选题A female-male mosaic fruit fly may be formed, if there is chromosome loss or______． A．equal division during sperm generation B．abnormal mitosis during merogenesis(fertilized egg cleavage) C．meiosis in embryo D．meiosis when sperm is tailed

单选题转导过程中产生的转导子，下面哪种说法对转导子的描述是正确的?( )

单选题豌豆黄色、圆粒品种与绿色、皱粒品种杂交，子二代表现9:3:3:1的子粒表型分离比例。这个比例是下列哪个群体的统计结果?______

单选题性导过程中起载体作用的是______。

单选题遗传物质的复制主要是在细胞分裂的______完成的。

单选题细菌中，同源重组发生在一些热点周围，这和( )在chi位点上的单链内切酶活性有关。

单选题______不能独立地复制DNA。

单选题用中性小菌落与分离型小菌落的酵母杂交，经减数分裂后所得子代分离比是______。

单选题真核细胞的染色质主要是由以下______成分构成的。

单选题农业生产中曾大量使用有机磷农药防治棉花害虫，使用多年后，发现害虫抗药性增强，导致这种现象的可能原因是______。 A．遗传漂移 B．害虫的迁移 C．基因突变和选择 D．自然进化

单选题______可以促进非严格配对的两段DNA发生重组。

单选题细菌杂交实验中，F因子和部分细菌染色体转移频率都比较高的杂交组合是______。

单选题某些个体在棕发中有一块白色或淡黄色的头发，这是哪一类突变造成的______。 A．性细胞突变 B．卵细胞突变 C．体细胞突变 D．配子突变