单选题以青霉素培养基做为选择培养基，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，只允许抗性型细菌在上生存 B．青霉素有时可补偿营养缺陷型，允许营养缺陷型细菌在基本培养上生存 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

单选题有人观察到玉米籽粒的一些性状(如籽粒颜色、紫色糊粉层、甜粒等性状)每年都以同样的频率发生相同的突变，这可以认为是突变的______。 A．重演性 B．平行性 C．可逆性 D．多方向性

单选题As with many a grown-up sporting star, the first hint of greatness came at an early age for Lewis Hamilton. As an eight-year-old at his first kart race, he charged "more like a mature driver than a novice," remembers Martin Hines, owner of the Zip Kart racing company. Scything his way through the field just outside London, Hamilton had a confident style that seemed different from normal rookies, Hines says. "There was a little spark about him." Now 22, and in his debut season in Formula One—he became the first black driver to make it onto the grid in motor racing's blue-ribbon championship. His success and profile that have earned young Hamilton comparisons with other sporting greats. His color— Hamilton's grandfather came to Britain from Grenada in the 50s—and the positive influence of his father, Anthony, have drawn parallels with Tiger Woods. Hamilton acknowledges that his participation could stoke interest among ethnic groups who may not be into the sport now. "Hopefully people that can relate to me will see that it's possible and also try to get into the sport," he told the BBC. Moreover, his youth, good looks and wholesome image are also likely to get marketers fired up. Countless more karting titles followed before 2001. He "made seasoned drivers look silly," says Tony Shaw, Hamilton's then team manager at Manor Motorsport. Hamilton's raw, natural speed and canny race craft nudged him closer to the big leagues. Hamilton's "understanding of when and where to overtake and how to take advantage of a situation is very advanced," Shaw says. At his first crack at GP2, the training ground for Formula One, Hamilton dominated the 2006 season with a series of blistering drives on his way to the title. Hamilton is "not worried about showing or doing what he's used to doing just because it's Formula One," says Hill. For many new drivers, "that's an enormous hurdle." With the retirement last year of seven-time world champion Michael Schumacher, there's one less rival for Hamilton to negotiate. And Hamilton is certainly not short on confidence. When he first met Ron Dennis—now his Formula One team boss—as a 10-year-old in a borrowed suit, Hamilton promptly told him he wanted to drive for McLaren. Three years later, he joined the team's support program for promising young drivers. But, say former team managers, he's ready to listen and learn when things go wrong. Hamilton has a rare "capacity to question himself—to analyze very clearly after a race," says Frederic Vasseur, general manager at the ART Grand Prix team behind Hamilton's GP2 championship. As for whether he'll become the Tiger Woods of the sport, it's too early to know whether he can live up to those standards. But for now, his fans are bullish. Damon Hill was the last British driver to take the world crown. And it's Hamilton, Hill says, "who looks likely to be the next./

单选题玫瑰冠与胡桃冠鸡杂交后代产生15只胡桃冠、14玫瑰冠、5只豌豆冠、6只单冠。已知纯种玫瑰冠与纯种豌豆冠鸡杂交后代是胡桃冠鸡，请选择

单选题纯种芦花雄鸡和非芦花母鸡交配，得到的子一代相互交配，子二代(F2)表现：______。 A．1/2芦花(♂)，1/2芦花(♀) B．1/2非芦花(♂)，1/2非芦花(♀) C．3/4芦花(♀♂)，1/4非芦花(♀♂) D．全为芦花(♂)，1/2非芦花(♀)1/2芦花(♀)

单选题两个基因A、B通常相距38cM，却在某生物染色体的同一臂上。在这38cM的区域内，大约有1/3的长度是一个臂内倒位。但这个倒位不包括这两个基因座。如果该植物是臂内倒位杂合子，这两个基因间的重组率如何?______。 A．大于38cM B．等于38cM C．小于38cM D．不能确定

单选题细菌中各种mRNA所编码的蛋白质数目常有差异，据此有monocistronic，polycistronic和intereistronic之分。多数mRNA是 a．monocistronic mRNA； b．polycistronic mRNA； C．intercistronic mRNA。

单选题一个AB血型的男人与一个B血型的女人结婚，生了4个孩子，第一个是AB型，第二个为O型，第三个为AB型，第四个为A型。后来，由于夫妻不和，丈夫提出离婚，声称经血型家系分析，他不可能是所有孩子的父亲，他说的有道理吗?______

单选题以下群体中下遗传率最大的是______。 A．F1群体 B．F2混合群体 C．F3混合群体 D．F4群体混合

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 在进行AB/ab′ab/ab测交时，如果有20％的卵母细胞在减数分裂时，a-b基因间形成了一个交叉节，测交后代中出现aaBb基因型的频率为。 A、10％ B、5％ C、20％ D、80％

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

单选题在减数分裂的前期Ⅰ的粗线期出现“十”字形图像，终变期形成“四体环”或“四体链”的个体应为______。 A．四体 B．同源四倍体 C．节段异源四倍体 D．相互易位杂合体

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