题干

在DNA 测序工作中,需要将某些限制性内切酶的限制位点在 DNA上定位,使其成为 DNA分子中的物理参照点。这项工作叫做“限制酶图谱的构建”。假设有以下一项实验:用限制酶 HindⅢ,BamHⅠ和二者的混合物分别降解一个 4kb(1kb即1千个碱基对)大小的线性DNA 分子,降解产物分别进行凝胶电泳,在电场的作用下,降解产物分开,如下图所示。

据此分析,这两种限制性内切酶在该DNA 分子上的限制位点数目是以下哪一组?(   )

A:HindⅢ1个,BamHⅠ2个

B:HindⅢ2个,BamHⅠ3个

C:HindⅢ2个,BamHⅠ1个

D:HindⅢ和BamHⅠ各有2个

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答案(点此获取答案解析)

A

同类题4

阅读下面短文,从短文后各题所给的四个选项(A、B、C和D)中,选出可以填入空白处的最佳选项。

    One of the easiest things in the world is to become a fault-finder. However, life can be 1when you are not busy finding fault with it.

    Several years ago I2a letter from seventeen-year-old Kerry, who described herself as a world-class fault-finder, almost always3by things. People were always doing things that annoyed her, and 4was ever good enough. She was highly self-critical and also found fault with her friends. She became a really 5person.

    Unfortunately, it took a horrible accident to change her 6.Her best friend was seriously hurt in a car crash. What made it almost 7to deal with was that the day before the8, Kerry had visited her friend and had spent the whole time criticizing her9of boyfriends, the way she was living, the way she related to her mother, and various other things she felt she needed to 10It wasn't until her friend was badly hurt that Kerry became 11her habit of finding fault. Very quickly, she learned to appreciate life rather than to 12everything so harshly ( 刻薄) . She was able to transfer her new wisdom to other parts of her13as well.

    Perhaps most of us aren't as extreme at fault-finding, 14when we're honest, we can be sharply 15of the world. I'm not suggesting you16problems, or that you pretend things are17than they are, but simply that you learn to allow things to be as they are—18most of the time, and especially when it's not a really big19.

    Train yourself to "bite your tongue" , and with a little20 you'll get really good at letting things go. And when you do, you'll get back your enthusiasm and love for life.