题目内容
假定基因a、b相互连锁，且发生交换的比率是20%，当AB/AB个体与ab/ab个体杂交，F1代的基因型如何F1代个体会产生何种配子各种配子的比例是多少若F1代个体进行自交，则后代中基因型及表型的比例如何
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Questions 57 to 61 are based on the following passage. People traveling long distances frequently have to decide whether they would prefer to go by land, sea, or air. Hardly can anyone positively enjoy sitting in a train for more than a few hours. Train compartments soon get cramped and stuffy. Reading is only a partial solution, for the monotonous rhythm of the wheels clicking on the rails soon lulls you to sleep. During the day, sleep comes in snatches. At night, when you really wish to go to sleep you rarely manage to do so. Inevitably you arrive at your destination almost exhausted. Long car journey are even less pleasant, for it is quite impossible even to read. On motorways you can, at least, travel fairly safely at high speeds, but more often than not, the greater part of the journey is spent on narrow, bumpy roads which are crowded with traffic. By comparison, trips by sea offer a great variety of civilized comforts. You can stretch your legs on the spacious decks, play games, swim, meet interesting people and enjoy good food—always assuming, of course, that the sea is calm. If it is not, and you are likely to get seasick; no form of transport could be worse. Even if you travel in ideal weather, sea journeys take a long time. Relatively few people are prepared to sacrifice up to a third of their holidays for the pleasure of traveling on a ship. Airplanes have the reputation of being dangerous and expensive. But nothing can match them for speed and comfort. Traveling at a height of 30,000 feet, far above the clouds, and at over 500 miles an hour is an exhilarating experience. For a few hours, you settle back in a deep armchair to enjoy the flight. The real escapist can watch a free film show and sip champagne on some services. But even when such refinements are not available, there is plenty to keep you occupied. An airplane offers you an unusual and breathtaking view of the world. You soar effortlessly over high mountains and deep valleys. You really see the shape of the land. If the landscape is hidden from the view, you can enjoy the extraordinary, sight of unbroken cloud plains that stretch out for miles before you, while the sun shines brilliantly in a clear sky. The journey is so smooth that there is nothing to prevent you from reading or sleeping. However you decide to spend your time, one thing is certain: you will arrive at your destination fresh and unctrumpled. By writing the passage, the author intends to ______.
假设磁盘上每个磁道划分成9个物理块，每块存放1个逻辑记录。逻辑记录R0，R1，…，R8存放在同一个磁道上，记录的安排顺序如表1-7所示。 表1—7记录的安排顺序 物理块 0 1 2 3 4 5 6 7 8 逻辑记录 R0 R1 R2 R3 R4 R5 R6 R7 R8 假定磁盘旋转一圈的时间为27ms，磁头当前处在R0的开始处。若系统顺序处理这些记录，使用单缓冲区，每个记录处理时间为3ms，则处理这9个记录的最长时间为 (11) ；若对信息存储进行优化分布后，处理9个记录的最少时间为 (12) 。
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