假设A、b代表玉米的优良基因，这两种基因是自由组合的．现有AABB，aabb两个品种，为培育出优良品种AAbb，可采用的方法如图所示．请根据图回答问题：（1）由品种AABB、aabb经过①、②、③过程

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假设A、b代表玉米的优良基因，这两种基因是自由组合的．现有AABB，aabb两个品种，为培育出优良品种AAbb，可采用的方法如图所示．请根据图回答问题：

（1）由品种AABB、aabb经过①、②、③过程培育出新品种的育种方式称为____ ，其原理是此过程中会出现____ ．应用此育种方式一般从____ 代才能开始选育AAbb个体，是因为____ ．

（2）若经过过程②产生的子代总数为1552株，则其中基因型为Aabb理论上有____ 株．基因型为Aabb的植株经过过程③，子代中AAbb与aabb的数量比是____ ．

（3）过程⑤常采用____ 技术得到Ab个体．与过程“①②③”的育种方法相比，过程⑤⑥的优势是____

（4）过程⑦育种方式是____ ，与过程⑦比较，过程④方法的明显优势是____ ．

上一题下一题 0.0难度选择题更新时间:2017-04-10 10:19:10

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                                                                                Just a Quick Nap 只要打个盹儿
      Do you feel a little sleepy after lunch? Well, that's normal. Your body naturally slows down then. What should you do about it? Don't reach for a coffee! Instead, take a nap.
       It's good to have a daily nap. First of all , you are more efficient（有效的） after napping . You remember things better and make fewer mistakes. Also, you can learn things more easily after taking a nap. A nap may increase your self-confidence（自信） and make you more active . It may even cheer you up. But, there are some simple rules you should follow about taking a nap. First, take a nap in the middle of day, about eight hours after you wake up. Next, a 20-minute nap is best. If you sleep longer, you may fall into a deep sleep. After waking from a deep sleep, you will feel worse. Also, you should set an alarm clock. That way, you can fully relax during your nap. You won't have to keep looking at the clock so you don't oversleep.
       Now，the next time you feel sleepy after lunch , don't get stressed . Put your head down, close your eyes, and catch forty winks.

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