图①示限制酶切割某生物DNA分子的过程；图②表示该生物体细胞部_爱下问搜题

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问题选择题

图①示限制酶切割某生物DNA分子的过程；图②表示该生物体细胞部分基因和染色体的关系；该生物的黑色素产生需要如图③所示的3类基因参与控制，三类基因的控制均表现为完全显性。下列说法正确的是

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A．图②所示的生物体中肯定存在含有2个a基因的细胞

B．用限制性内切酶可以从图②所示基因型的细胞中提取合成黑色素的所有目的基因

C．若图③中的1个b基因突变为B，则该生物体仍然可以合成出物质乙

D．图①所示限制酶能识别的碱基序列及切点是TTAA，切点在G和A之间

答案

答案：A

完形填空

The best gift I’ve received was from two young boys. At that time, I didn’t have a lot of money or a huge home. As a single mom with three young children of my own, life is so    .
They were boys with dirty faces a bit older than my children, but they always     my yard. I must feed my children who were       thirsty and hungry, so I      a lot of time baking so many healthy muffins（松饼）.These two boys almost grew up in our yard, and they were glad to pray with us before they would have a        with my family.
We would also     food, laughter, books and games with them. And a while later, they       . I didn’t know where they had gone and I often wondered what had     in their lives, and meanwhile I hoped for the best.
During one of the darkest times in my personal life, no one came to visit me. I felt really lonely these days. I even wondered if God had       me. On Mother’s Day, my children    home from school. We were sitting together talking when I heard a     on the door.
I went to answer it, and there stood two clean-faced, tall, smiling boys holding two bundles of beautiful flowers I had ever seen. They said to me “Do you        us? You used to feed us muffins! They were so        . We wanted to come back and thank you and say Happy Mother’s Day     you were really like a       to us!” I was so moved that I couldn’t help crying, and thankedthem again and again.

C．interesting

D．disappeared

填空题

常见的脓耳变证有______、______和______。