问题 解答题

下列是男女成对染色体排序图.

请分析作答:

(1)显示为男性的是哪幅图?

(2)决定女性性别的基因位于哪一对染色体上?

(3)组成染色体的物质是什么?

答案

(1)分析图示可知:甲图中的第23对染色体一条大、一条小,为XY染色体,因此甲图表示男性的体细胞中的染色体的组成;乙图中的第23对染色体形态大小基本相同,是XX染色体,即乙图表示的是女性体细胞中的染色体的组成.

(2)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.例如,人类有22对常染色体,1对性染色体.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.因此决定女性性别的基因位于XX染色体(或第23对染色体).

(3)染色体是细胞内具有遗传性质的物体,易被碱性染料染成深色,所以叫染色体(染色质);染色体是细胞核中载有遗传信息(基因)的物质,主要由脱氧核糖核酸(DNA)和蛋白质组成,如图

每一种生物细胞内染色体的形态和数目是一定的,染色体数目的恒定对生物正常的生活和传种接代是非常重要的.DNA的结构像一个螺旋形的梯子,DNA上具有遗传效应的片段是基因.

故答案为:

(1)甲图;

(2)XX染色体(或第23对染色体);

(3)DNA和蛋白质.

选择题
完形填空

Marriage is still a popular institution in the United States, but divorce(离婚) is becoming_1_as“popular”.Most American people get married, _2_,at the present time, and fifty percent of American marriages end _3_ divorce. However, four out of five divorced people do not _4_ single. They get married a second time to _5_ partners. Sociologists(社会学家)tell us that in the next century, _6_American people will marry three _7_ four times in one lifetime. Alvin Toffler, an American sociologist, _8_this new social form serial(连续的)marriages. In his book Future Shock, Toffler gives many _9_ for this change in American marriage. In modern society, _10_ lives don't stay the same for very long.Americans_11_ change their jobs, their homes, and their circles of _12_So,the person who was a _13_ husband or wife ten years ago is sometimes not as good ten years _14_After some years of marriage, a husband and wife can _15 _that their lives have become very different, and they don't 16the same interests anymore. For this reason, Toffler says, people in the twenty first century will not _17_ to marry only one person for an _18_ lifetime. They will plan to stay married to one person for perhaps five or ten years, and then marry _19_.Most Americans will expect to have a “marriage carrier”that _20_ three or four marriages.

1. A. already           B. almost          C. ever        D. even

2. A. anyway           B. then            C. but         D. therefore

3. A. with            B. from            C. in          D. for

4. A. live              B. take            C. make       D. stay

5. A .new             B. old              C. young       D. pretty

6. A. most             B. main            C. few         D. mostly

7. A. and             B. by              C. or          D. to

8. A. asks             B. calls             C. tells        D. lets

9. A. causes           B. chances           C. problems    D. reasons

10. A. human's         B. people's          C. person's      D. man's

11. A. frequently       B. quickly           C. rapidly      D. fast

12. A. parents         B. classmates         C. neighbors    D. friends

13. A. polite           B. strict              C. good      D. unfriendly

14. A. late             B. latter           C. lately       D. later

15. A. imagine         B. feel              C. believe     D. suppose

16. A. enjoy           B. hold             C. divide      D. share

17. A. desire          B. plan              C. wish       D. design

18. A. entire         B. extreme           C. total       D. whole

19. A. the other       B. others             C. other       D. another

20. A. appears        B. happens           C. includes     D. carries