单选题Back in the 1870s, Charles Darwin's cousin Francis Galeton wanted to define the face of a criminal. He assembled photographs of men convicted of heinous crimes and made a composite by lining them up on a single photographic plate. The surprise: everybody liked the villain, including Galton himself. He reasoned that the villainous irregularities he supposed belonged to criminal faces had disappeared in the averaging process. In the next century, scientists began to show reliably that faces combined digitally on computers were likable—more so than the individual faces from which they were composed. Although people clearly admire the long legs of Brazilian model Ana Hickmann or Dolly Parton's breasts, in general humans like averages. Researchers confirmed that humans judge real faces by their differences or similarities from a norm. But they also found that the norm can change quickly: When researchers showed 164 people sets of 100 computer-generated faces representing a slow transition from male to female—and from Japanese to Caucasian—it turned out that the test subjects' idea of what constitute an "average" face shifted depending on the first face they saw. When they were flashed a super masculine face first, more faces on the spectrum impressed them, by contrast, as female. The masculine face had, in effect, set a standard. From then on, other faces had to be more masculine in order to rate as belonging to the gender. The study noted a similar shift using a scale of faces moving from surprise to disgust. The authors, who published their results in the journal Nature, conclude that in real life we also quickly change ore" perception of the midpoint—what's normal—depending on what we see. We may not be aware that our judgment has changed; we simply see differently, says Michael Webster, a psychologist at the University of Nevada in Reno and coauthor of the study. One implication is that individual and social attitudes toward what's acceptable, and what's beautiful, change over time. "If you look at plastic-surgery trends, in the 1950s and 1960s you saw little upturned noses," notes Harvard psychologist Nancy Etcoff, author of the book Survival of the Prettiest : The Science of Beauty. "Now the noses are broader and the lips are plumper. We're seeing images from around the globe, and it's changing our idea of the average. " So if you're unhappy with some aspect of your face, take comfort: beauty is a moving target.

单选题tRNA的反密码子能识别mRNA的密码子。反密码子的第一碱基能识别一个以上的密码子第三碱基(wobbling)者为 a．A； b．A和C； c．U和G； d．C。

单选题入噬菌体的裂解途径是由以下哪个蛋白基因控制? ____ 。

单选题原核mRNA的Shine-Dalgarno顺序通常是 a．多嘧啶序列； b．多嘌呤序列； c．嘌呤和嘧啶基本各半。

单选题自然选择学说不能解释( )。

单选题具有一对相对性状的亲本杂交后，子代中只表现一个亲本的性状，这种遗传现象称为______。 A.完全显性 B.不完全显性 C.共显性 D.超显性

单选题转化、转导和性导的相同点在于______。 A.都需要噬菌体 B.都引起基因重组 C.都需要F因子 D.不引起重组

单选题Pedigree method or somatic cell hybridization can be used to map human chromosome genes. When the former is used to do chromosome mapping? ______. A．X chromosome linked genes are easier than somatic genes B．X chromosome linked genes are more difficult than somatic genes C．X chromosome linked genes are as easy as somatic genes D．All the above statements are incorrect because the data of pedigree method is unable to be used in chromosome mapping

单选题有一个杂交组合AaBbCc×AaBbCc，三个位点都是独立遗传并呈完全显性，那么在其后代中与亲代表现型完全相同的个体的概率是(假定未发生新的突变，也无更复杂的因子)______

单选题异序性是指：______。 A．T4噬菌体的环状排列基因次序模型 B．遗传重组时非姐妹染色单体之间形成的Holliday中间体交叉迁移造成的DNA双链异源性 C．由于倒位产生的融合基因表达的性状嵌合性 D．由于线粒体在细胞分裂中的无序性而造成的机体内各组织间遗传上的异质性

单选题下列哪一项不包括在生物多样性中?( )

单选题The biggest demonstration in a generation is being assembled by mobilizing the power of the web, which allows anti-war groups to rally multitudes at the click of a mouse. Cornish speakers for peace can share ideas by e-mail with Rhodes Scholars Against the War while taking into account the sensitivities of the Young Muslim Sisters. Footsore ban-the-bomb veterans such as Tony Myers of the Campaign for Nuclear Disarmament, busily preparing yesterday for the mass protest, can only marvel at the power of the net. "It's made a massive difference," he said. "Back in the 1980s when we were trying to organize huge demos it was all about going to meetings and sending mail to regional people. I was a volunteer before the 1983 demonstration which attracted 400,000 marchers. The office was just awash with people printing things on old duplicators. People today feel more like they are part of a big movement. In the 1980s, we would read about demos all over the world a few days later in the newspapers. Now you know all the details in advance if you are on the e-mail list. The Stop the War Coalition needs only a handful of headquarters staff because the website is a virtual campaign group in itself, complete with briefings, news, addresses and artwork. Children's superior mastery of the internet is reflected in the proliferation of youth groups opposing war. The Woodcraft Folk (a sort of pacifist version of the Scouts) announce that they will be bringing an orange parachute on the march. The Engels-Marx Communist Party (slogan "Resist and Revolt") is a group of pupils at a Leicester comprehensive school opposing the war. The entire country is covered from the Aberdeen Students Against War Society to Torbay Stop the War group. Anti-war campaigners put leaflets, maps, posters and petitions on their websites for supporters to print, stick in their window or hand out at the march. Stop the War Coalition includes a direct- debit form which supporters can download and send to their bank manager to make donations. Message boards are filled with anti-war protesters arguing their case. The issue is being exploited by the British National Party, which has posted a self-serving press release proclaiming support for the march because of their concerns over "the power of the Israeli lobby". Anti-war individuals have been e-mailing friends with songs for the march, one to the tune of If You're Happy and You Know It. The internet was created in the 1960s partly by the Advanced Research Project Agency of the US Department of Defense. It is widely said to have been created in order to send military messages after an atomic war.

单选题一项调查表明，由正常双亲生的735000个孩子中，有14人为短指、趾畸形。已知短指、趾畸形是显性性状，则短指、趾畸形的突变率为______。 A．10-4 B．2×10-5 C．2×10-4 D．10-5

单选题三体通常以______来表示。 A．2n-1 B．2n+3 C．2n+1

单选题氨酰tRNA靠它的反密码子识别mRNA的密码子，对于终止密码子UAA、UAG和UGA来说 a．氨酰tRNA仅识别UAA； b．氨酰tRNA仅识别UAG； c．氨酰tRNA可识别所有终止密码子； d．氨酰tRNA均不识别。

单选题The human Y chromosome—the DNA chunk that makes a man a man—has lost so many genes over evolutionary time that some scientists have suspected it might disappear in 10 million years. But a new study says it'll stick around. Researchers found no sign of gene loss over the past 6 million years, suggesting the chromosome is "doing a pretty good job of maintaining itself," said researcher David Page of the Whitehead Institute for Biomedical Research in Cambridge, Mass. That agrees with prior mathematical calculations that suggested the rate of gene loss would slow as the chromosome evolved, Page and study co-authors note in Thursday's issue of the journal Nature. And, they say, it clashes with what Page called the "imminent demise" idea that says the Y chromosome is doomed to extinction. The Y appeared 300 million years ago and has since eroded into a dinky chromosome, because it lacks the mechanism other chromosomes have to get rid of damaged DNA. So mutations have disabled hundreds of its original genes, causing them to be shed as useless. The Y now contains only 27 genes or families of virtually identical genes. In 2003, Page reported that the modern-day Y has an unusual mechanism to fix about half of its genes and protect them from disappearing. But he said some scientists disagreed with his conclusion. The new paper focuses on a region of the Y chromosome where genes can't be fixed that way. Researchers compared the human and chimpanzee versions of this region. Humans and chimps have been evolving separately for about 6 million years, so scientists reasoned that the comparisons would reveal genes that have become disabled in one species or the other during that time. They found five such genes on the chimp chromosome, but none on the human chromosome, an imbalance Page called surprising. "It looks like there has been little if any gene loss in our own species lineage in the last 6 million years," Page said. That contradicts the idea that the human Y chromosome has continued to lose genes so fast it'll disappear in 10 million years, he said. "I think we can with confidence dismiss … the 'imminent demise' theory," Page said. Jennifer A. Marshall Graves of the Australian National University in Canberra, a gene researcher who argues for eventual extinction of the Y chromosome, called Page's work "beautiful" but said it didn't shake her conviction that the Y is doomed. The only real question is when, not if, the Y chromosome disappears, she said. "It could be a lot shorter than 10 million years, but it could be a lot longer," she said. The Y chromosome has already disappeared in some other animals, and "there's no reason to expect it can't happen to humans," she said. If it happened in people, some other chromosome would probably take over the sex-determining role of the Y, she said.

单选题有一个水稻不育系与恢复系杂交，然后让F1自交，结果发现其F2代群体全部散粉，但其中一半植株花粉半不育。则其不育系类型为______。 A．孢子体不育 B．配子体不育 C．核不育 D．质不育

单选题已知D、E、F三基因位点连锁，且在染色体上的顺序为DEF，D和E相距20个遗传 单位，正和F也相距10个遗传单位。用杂交组合为DDEEFFxddeeff的子代进行测交，发现测交子代表型中有2％f!,~JDdeeFf和2％的ddEeff，根据以上资料可以推知，此区段的符合系数(并发系数)为