问题 问答题

哺乳动物中,从亲代遗传来的基因是差异表达的,这种现象的理论基础是什么

答案

参考答案:在精子或卵子发生过程中一些基因被关闭或者被甲基化。如IGFⅡ基因在卵母细胞中被甲基化,因此来自于母本的等位基因在后代中不表达。来源于父本的等位基因没有甲基化,它能够表达。其他一些基因在精母细胞中被甲基化,对这种基因来说,来源于母本的等位基因能够表达。

阅读理解

阅读理解。

     When you are learning a language, listening, speaking and writing are important,   but reading can  also

be very helpful. When you read,  you can not only learn some new words, but also learn how to use them. When you read a passage, it gives you a good example for writing. Here are some good reading tips.

     Firstly, try to read at the right level (水平). Read something that you can understand.  If it is too  hard

for you, it is not interesting.

     Secondly, try to understand the new words.  If there are four or five new words on a page,  don't  use

a dictionary.  Instead, try to guess their meanings as you read.   Mark (作标记) them with a pencil. Then

look them up in a dictionary when you finish reading,   and write them in your own vocabulary book.  Try

to remember them.

     Thirdly, try to read for a short time once a day. Fifteen minutes or half an hour every day is better than

two hours every Sunday.   For example,   you can read before you go to bed,   or after you get up  or  at

lunchtime.

     Lastly, read something that interests you. Choose a newspaper, a book or a magazine about a subject

that you like. It will be easy enough for you to understand.

1. The underlined word "tips" in the passage means "_____  " in Chinese.

A. 末端        

B. 小费        

C. 处所      

D. 建议

2. How many reading tips does the writer give us?

A. Six.          

B. Five.        

C. Four.      

D. Three.

3. If you meet a few new words on a page while reading, you can _____  .

A. stop reading

B. guess the meanings at first

C. write them down at once

D. look them up right away

4. Which of the following is TRUE according to the passage?

A. Reading a lot can help you write better.

B. It is useful for you to read for long once a week.

C. When you read, you can only learn some new words.

D. Try to read something hard to make your English better.

5. Which is the BEST title for the passage? 

A. How to look up a new word    

B. How to make reading better    

C. How to remember new words

D. How to choose something to rea

填空题