题干

减数分裂过程中可能发生的变异及其原因分析,错误的是(  )

A:基因突变;减数第一次分裂前的间期受到一些辐射等外界因素的诱导

B:基因重组;四分体中的非姐妹染色单体发生了交叉互换或减数第一次分裂后期非同源染色体自由组合

C:染色体结构的变异;染色体的片段缺失、重复、倒位或易位

D:染色体数目的变异;经秋水仙素处理后,中心体无法复制,导致纺锤体无法形成

上一题 下一题 0.0难度 选择题 更新时间:2018-11-23 02:58:47

答案(点此获取答案解析)

D

同类题5

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项,其中有一项为多余选项。

    Growing up is not always easy. When we face difficulties, we should never give up. We should try our best to make the life better. It is not useful to cry for help. Hong Zhanhui's story of growing from boy to man tells us about this.

    Hong was born in 1982 in a poor family in Henan Province. When he was only 11, his father became badly ill. And one day he came back with a baby girl. The girl was very young and they must spend much time looking after her. However, a year later, Hong's mother left home.____ So everything fell onto the young boy:to take care of his father and the sister, and to go on to study.

    Although his life was very hard, Hong didn't go away from his father and sister.____. He climbed tall trees to get birds' eggs for his sister. He walked two hours at weekends to the market to buy different things. Then he sold the things around his school to make some money.

    ____. To take care of his sister, he worked hard to rent(租) a room near his college for her, and sent her to school every day.

    When people knew Hong's story, he became a hero in people's eyes. Many people wanted to help him. But Hong refused the help from others. He said he felt happy by other's help, but he believed he could take care of his family by himself.____.

A. He worked in a part-time job to look after his family.

B. His life was hard, but he has grown up from boy to man.

C. A few years later, he began to study at a college.

D. She no longer wanted to live such a poor life and face her sick husband.

E. Because of the hard life, he felt sad and wanted to give up.