问题 问答题

何谓缺失如何分类

答案

参考答案:缺失是染色体片段的丢失,缺失使位于这个片段的基因也随之发生丢失。按染色体断点的数量和位置可分为末端缺失和中间缺失两类:①末端缺失指染色体的臂发生断裂后,未发生重接,无着丝粒的片段不能与纺锤丝相连而丢失;②中间缺失指一条染色体的同一臂上发生了2次断裂,2个断点之间的片段丢失,其余的2个断片重接。

阅读理解

The summer vacation is over. It is true that time always flies fast. During the vacation , the weather was bad and I could not do much work, but I live happily.

As the afternoon was hot, I did my work in the morning. I used to get up at 6:30 and take a walk in the garden for half an hour. After breakfast, I began reading English and Chinese and did some exercises in maths. This took me three hours or more. I worked quite hard and made good progress.

I spent the afternoon outside. I went to swim and it was very funny. I would not go home until it was five or six o’clock. Sometimes a friend would come to see me and we would spend some hours listening to music.

In this way, I spent my vacation happily. And I not only studied well but also became a good swimmer. Now I am in good health and high spirits.

60. What does the text tell us?

A. How the writer spent his summer vacation.

B. What the weather was like in the summer.

C. When the writer got up in the morning.

D. Where the writer took a walk.

61.The writer spent most of the afternoon _______.

A. listening to music    B. visiting his friends    C. walking in the garden   D. swimming 

62. The writer had very good summer holidays because he ______.

A. worked very hard and made good progress

B. learned to swim and did his work well

C. got up early and went home late

D. liked swimming better than studying

63.Which of the following is NOT true?

A. The writer made progress in his lesson.

B. The writer took a walk for half an hour before breakfast

C. The writer began studying as soon as as he got up.

D. The writer spent more time swimming than listening to music.

单项选择题