单选题小黑麦是我国科技工作者用普通小麦和黑麦杂交。将获得的种间杂种进行染色体加倍而育成的异源多倍体，目前已在云贵高原的高寒地带种植，表现了一定的增产效果。它的遗传组成为______。 A．2n=4x=ABDR=28 B．2n=6x=AABBRR=42 C．2n=5x=AABBDDR=35 D．2n=8x=AABBDDRR=56

单选题最早用果蝇为材料发现性连锁遗传的科学家是______，发现果蝇的X染色体不分离现象并直接证明遗传的染色体学说的科学家是______。

单选题一个表型正常的人，其舅父患某种常染色体隐性遗传病，他如果和表型正常的姨表妹结婚，后代中患该病的风险是______。

单选题A very important world problem, if not the most serious of all the great world problems which affect us at the moment, is the increasing number of people who actually inhabit this planet. The limited amount of land and land resources will soon be unable to support the huge population if it continues to grow at its present rate. In an early survey conducted in 1888, a billion and a half people inhabited the earth. Now, the population exceeds five billion and is growing fast--by the staggering figure of 90 million in 1988 alone. This means that the world must accommodate a new population roughly equal to that of the United States and Canada every three years! Even though the rate of growth has begun to slow down, most experts believe the population size will still pass eight billion during the next 50 years. So why is this huge increase in population taking place? It is really due to the spread of the knowledge and practice of what is becoming known as "Death Control". You have no doubt heard of the term "Birth Control"--" Death Control" is something rather different. It recognizes the work of the doctors and scientists who now keep alive people who, not very long ago, would have died of a variety of then incurable diseases. Through a wide variety of technological innovations that include farming methods and sanitation, as well as the control of these deadly diseases, we have found ways to reduce the rate at which we die--creating a population explosion. We used to think that reaching seventy years old was a remarkable achievement, but now eighty or even ninety is becoming recognized as the normal life-span for humans. In a sense, this represents a tremendous achievement for our species. Biologically this is the very definition of success and we have undoubtedly become the dominant animal on the planet. However, this success is the very cause of the greatest threat to mankind. Man is constantly destroying the very resources which keep him alive. He is destroying the balance of nature which regulates climate and the atmosphere, produces and maintains healthy soils, provides food from the seas, etc. In short, by only considering our needs of today, we are ensuring there will be no tomorrow. An understanding of man's effect on the balance of nature is crucial to be able to find the appropriate remedial action. It is a very common belief that the problems of the population explosion are caused mainly by poor people living in poor countries who do not know enough to limit their reproduction. This is not true. The actual number of people in an area is not as important as the effect they have on nature. Developing countries do have an effect on their environment, but it is the populations of richer countries that have a far greater impact on the earth as a whole. The birth of a baby in, for example, Japan, imposes more than a hundred times the amount of stress on the world's resources as a baby in India. Most people in India do not grow up to own cars or air-conditioners--nor do they eat the huge amount of meat and fish that the Japanese child does. Their life-styles do not require vast quantities of minerals and energy. Also, they are aware of the requirements of the land around them and try to put something back into nature to replace what they take out. For example, tropical forests are known to be essential to the balance of nature yet we are destroying them at an incredible rate. They are being cleared not to benefit the natives of that country, but to satisfy the needs of richer countries. Central American forests are being destroyed for pastureland to make pet food in the United States cheaper; in Papua New Guinea, forests are destroyed to supply cheaper cardboard packaging for Japanese electronic products; in Burma and Thailand, forests have been destroyed to produce more attractive furniture in Singapore and Japan. Therefore, a rich person living thousands of miles away may cause more tropical forest destruction than a poor person living in the forest itself. In short then, it is everybody's duty to safeguard the future of mankind--not only through population control, but by being more aware of the effect his actions have on nature. Nature is both fragile and powerful. It is very easily destroyed; on the other hand, it can so easily destroy its most aggressive enemy--man.

单选题纯种芦花雄鸡和非芦花母鸡交配，得到子一代。子一代个体互相交配，问子二代的芦花性状与性别的关系是______。

单选题Who won the World Cup 1994 football game? What happened at the United Nations? How did the critics like the new play? (1) an event takes place, newspapers are on the streets (2) the details. Wherever anything happens in the world, reporters are on the spot to (3) the news. Newspapers have one basic (4) , to get the news as quickly as possible from its source, from those who make it to those who want to (5) it. Radio, telegraph, television, and (6) inventions brought competition for newspaper. So did the development of magazines and other means of communication. (7) , this competition merely spurred the newspapers on. They quickly made use of the newer and faster means of communication to improve the (8) and thus the efficiency of their own operations. Today more newspapers are (9) and read than ever before. Competition also led newspapers to branch out into many other fields. Besides keeping readers (10) of the latest news, today's newspapers (11) and influence readers about politics and other important and serious matters. Newspapers influence readers' economic choices (12) advertising. Most newspapers depend on advertising for very (13) . Newspapers are sold at a price that (14) even a small fraction of the cost of production. The main (15) of income for most newspapers is commercial advertising. The (16) in selling advertising depends on a newspaper's value to advertisers. This (17) in terms of circulation. How many people read the newspaper? Circulation depends (18) on the work of the circulation department and on the services or entertainment (19) in a newspaper's pages. But for the most part, circulation depends on a newspaper's value to readers as a source of information (20) the community, city, county, state, nation, and world—and even outer space.

单选题 在碱基置换中，嘌呤碱基与嘧啶碱基的置换现象，称为（ ）。 A、转换　　B、颠换　　C、移码突变　　D、插入

单选题DNA聚合酶Ⅲ的描述中哪项不正确?( )

单选题玉米n+1的花粉不育，n+1的胚囊可育，已知R产生红色，r无色。在杂交RRr♀×rr♂中子代的表现型比例是______。 A．1红:1无 B．3红:1无 C．5红:1无 D．6红:1无

单选题Holliday中间体在( )过程中产生。

单选题Watson和Crick在1953年提出( )。

单选题在噬菌体的蛋白质外壳中含有______。

单选题DNA双螺旋结构模型的描述中哪一条不正确?______

单选题 人类的秃顶属于（ ）。 A、从性性状　　B、伴性遗传　　C、限性性状　　D、半合基因

单选题以病毒颗粒为载体将遗传物质从一个细胞转移到另一个细胞的过程称为______。

单选题在做E.coli的转化实验时，要使E.coli处于感受状态，常用一种无机化合物处理，它是______。

单选题原核细胞遗传物质集中在细胞的一个或几个区域中，密度较低，与周围的细胞质无明确的界限，称作______。

单选题DNA解链(熔解)温度Tm决定于 a．A-T碱基对的比例； b．G-C碱基对的比例； c．A-T碱基对的比例和DNA变性条件； d．G-C碱基对的比例和DNA变性条件。

单选题侵染甲细菌后的噬菌体再去侵染另一种乙细菌，结果发生了甲乙细菌的基因重组，这是______。 A．转化 B．接合 C．转导 D．性导

单选题对于一个隔离的且数量已经大为减少的种群来说，其潜在的危险是( )。