问题 选择题

女子卵细胞的基因组成可以表示为(  )

A.22条+Y

B.44条+XY

C.22条+X

D.44条+XX

答案

人类体细胞内染色体分为常染色体和性染色体.常染色体就是对性别决定不起直接作用,除了性染色体外的所有染色体.人类正常染色体为46条(23对),其中22对称为常染色体,男女都一样;第23对称为性染色体,人的性别主要是由性染色体决定的,男性体细胞中的一对性染色体组成是XY,女性体细胞中的一对性染色体组成是XX.在亲代的生殖细胞形成过程中,经过减数分裂,染色体彼此分离,男性产生两种类型的精子--含22条+X染色体的精子和含22条+Y染色体的精子.女性则只产一种含22条+X染色体的卵细胞.受精时,如果是含22条+X的精子与卵子结合,就产生具有44条+XX的受精卵并发育成女性;如果是含22条+Y的精子与卵子结合,就产生具有44条+XY的受精卵并发育成为男性.因此;女性卵细胞的染色体组成可表示为22条+X.

故选C

阅读理解

阅读理解。

     Bill Gates was born in 1955. He grew up in Seattle, Washington. When he was young, he was good at

science and maths. And he wanted to be a scientist.

     Bill started to play with computers when he was 13. At that time, computers were very large machines.

Once he was interested in a very old computer. He and some of his friends spent lots of time doing unusual

(不寻常的) things with it. In the end, they worked out a software ( 软件) program with the old machine. Bill

sold it for 4200 dollars when he was only 17.

     In 1973, Bill went to Harvard University (哈佛大学). He developed the Basic language for the first

microcomputer (微型电子计算机). In his third year, he left Harvard. Bill began his company in 1975 with his

friend Paul Allen. They thought that the computer would be a very important tool in every office and in every

home, so they began developing software for personal computers. They developed the software to make it

easier for people to use computers.

     In 1999, Bill wrote a book. In the book, he told people how computer technology could solve business

problems in new ways. It was one of the best-sellers on The New York Times' list. Bill Gates has many

hobbies. He enjoyed reading very much. He also enjoys playing golf and bridge.

1. When did Bill begin to play with computer?

A. In 1965.

B. In 1966.

C. In 1968.

D. In 1972.

2. How old was Bill when he went to Harvard University?

A. 17 year sold

B. 18 year sold

C. 19 year sold

D. 20 year sold

3. Bill left Harvard University when he was a _____.

A. first-year student

B. second-year student

C. third-year student

D. fourth-year student

4. Bill wrote a book about _____.

A. how to do unusual things

B. how to play computer games.

C. how to work out a software program

D. how to solve business problems with the help of computer in new ways

5. We can learn from the text that _____.

A. Bill worked for Microsoft before he went to Harvard University

B. Bill sold his first software program for 420 dollars

C. Bill began his company in 1976 with his friend

D. reading is one of Bill's hobbies

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