单选题家猫中有一位于常染色体上的基因杂合时，呈现无尾性状(只在骨盆上有痕迹)，而在纯合体时，又是致死的，那么当一无尾猫与另一无尾猫杂交时，子代表型为______

单选题在一个岛上，1999年的种群中，二倍体植物的等位基因Aa的频率为p(A)=0.90，q(a)=0.10，如假定2000年种群数仅为50，那么2000年失去等位基因a[p(A)=1]的概率是什么?

单选题One of the most important social developments that helped to make possible a shift in thinking about the r01e of public education was the effect of the baby boom of the 1950s and 1960s on the schools. In the 1920s, but especially in the Depression conditions of the 1930s, the United States experienced a declining birth rate—every thousand women aged fifteen to forty-four gave birth to about 118 live children in 1920, 89.2 in 1930, 75.8 in 1936, and 80 in 1940. With the growing prosperity brought on by the Second World War and the economic boom that followed it, young people married and established households earlier and began to raise larger families than had their predecessors during the Depression. Birth rates rose to 102 per thousand in 1946, 106.2 in 1950, and 118 in 1955. Although economics was probably the most important determinant, it is not the only explanation for the baby boom. The increased value placed on the idea of the family also helps to explain this rise in birth rates. The baby boomers began streaming into the first grade by the mid-1940s and became a flood by 1950. The public school system suddenly found itself overtaxed. While the number of schoolchildren rose because of wartime and postwar conditions, these same conditions made the schools even less prepared to cope with the flood. The wartime economy meant that few new schools were built between 1940 and 1945. Moreover, during the war and in the boom times that followed, large numbers of teachers left their profession for better-paying jobs elsewhere in the economy. Therefore, in the 1950s and 1960s, the baby boom hit an antiquated and inadequate school system. Consequently, the "custodial rhetoric" of the 1930s and early 1940s no longer made sense; that is, keeping youths aged sixteen and older out of the labor market by keeping them in school could no longer be a high priority for an institution unable to find space and staff to teach younger children aged five to sixteen. With the baby boom, the focus of educators and of laymen interested in education inevitably turned toward the lower grades and back to basic academic skills and discipline. The system no longer had much interest in offering nontraditional, new, and extra services to older youth.

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A commonplace in genetics is the relationship between recombination frequency and crossover value. Generally speaking, ______. A．recombination frequency may be directly obtained according to phenotypic ratios, but crossover value cannot be directly obtained according to phenotypic ratios B．crossover value may be replaced by recombination frequency or chiasm frequency you get from the observation under microscope when genetic distance is considerably short C．crossover value may be replaced by recombination frequency when genetic distance is as a medium value, not too long and not too short D．recombination frequency will be very different from crossover value when there is a third locus in between the two loci you analysed

单选题对一生物减数分裂进行细胞学检查，发现后期Ⅰ出现染色体桥，表明该生物可能含有______。 A．臂间倒位染色体 B．相互易位染色体 C．臂内倒位染色体 D．顶端缺失染色体

单选题序列(IS)编码 ____ 。

单选题在20世纪30年代，对于生物进化过程中遗传和变异的研究，已经从( )。

单选题有人用菜豆作实验材料，用一个有色、大粒品系和另一白色、小粒品系杂交，得到的结果是：有色PP，45株，种子平均质量(0.307±0.05)kg；中间色Pp，80株，种子平均质量(0.283±0.03)kg；白色pp，41株，种子平均质量(0.264±0.05)kg。产生这些差异的可能原因是( )。

单选题以青霉素培养基作为选择培养基，用来筛选细菌的营养缺陷型，这一技术的原理是______。 A．青霉素可杀死敏感型细菌，只允许抗性细菌生存 B．青霉素有时可以补偿营养缺陷型，允许营养缺陷性细菌在基本培养基上生存 C．青霉素在营养缺陷型的菌落特征上，起明显的修饰作用，便于人们观察认识 D．青霉素可杀死繁殖的原养型细菌，只留下营养缺陷型

单选题下列何种杂交可引起λ噬菌体裂解细菌细胞______ A.Hfr(λ)×F- B.Hfr×F-(λ) C.Hfr×F D.Hfr(λ)×F-(λ) E.上述答案都不对

单选题隐性上位发生的情况下，一般在：F2中的表型比为______。 A.9:3:3:1 B.9:3:4 C.15:1 D.9:7

单选题细菌抗药性的提高是由下列哪种原因造成的?( )

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?

单选题下面是关于现代生物进化理论的叙述，其中不正确的是( )。

单选题有两个细菌品系，它们合成三种氨基酸的能力不同，以a+b+c+为供体和受体a-b-c-杂交。杂交后，取细菌的悬浮液分别涂在补充了氨基酸A、B和C的培养基上，观察到在一种平板上有四种细菌菌落，然后把此菌落影印到各种平板上(如图所示)根据上述资料，下列有关各菌落基因型的阐述哪句话正确______A．菌落②的基因型一定是a-b+c-B．菌落③的基因型一定是a+b+c+C．菌落④的基因型一定是a-b-c-D．上述答案均对

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.

单选题一个处于平衡状态的植物群体中的白化苗的频率约是4×10-4，白化基因是隐性的，那么表现型正常的植株后代中出现白化苗的频率是()。

单选题在一个突变过程中，一对额外的核苷酸插入DNA内，会有什么样的结果? (a)完全没有蛋白产物；(b)产生的蛋白中有一个氨基酸发生变化； (c)产生的蛋白中有三个氨基酸发生变化； (d)产生的蛋白中有两个氨基酸发生变化； (e)产生的蛋白中，插入部位以后的大部分氨基酸都发生变化。

单选题小鸡中，两对独立遗传的基因控制着羽毛色素的产生和沉积，在一个位点上，显性基因可产生色素，隐性基因则不产生色素；在另一位点上，显性基因阻止色素的沉积，隐性基因则可使色素沉积。小鸡羽毛的着色，必须能产生并沉积色素，否则为白色毛。如果一表现型为白色的鸡(两位点均为隐性纯合体)和另一种表现型为白色的鸡(两位点均为显性纯合体)进行杂交，F 2 代中羽毛着色的频率为______