题干

金银花的有效成分为绿原酸,具有广泛的杀菌、消炎功能,其结构简式如图.下列有关绿原酸的说法中不正确的是(   )

A:绿原酸分子中有4个手性碳原子

B:绿原酸能发生显色反应、取代反应和加成反应

C:每摩尔绿原酸最多与4 mol NaOH反应

D:绿原酸分子中所有碳原子都能在同一平面上

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答案(点此获取答案解析)

D

同类题2

野生型果蝇的眼形是圆眼,某遗传学家在研究中偶然发现一只棒眼雄果蝇,他想探究果蝇眼形的遗传特点,便设计了如图甲所示的实验(亲代果蝇均系纯合子).雄果蝇的染色体组成图及性染色体分区段如图乙所示.据图分析回答下列问题:

(1)若F2中圆眼:棒眼=3:1,则该对性状受一对等位基因控制,____ 是显性性状.若F2中圆跟:棒眼=27:37,则该对性状受____ 对等位基因控制.

(2)若该对性状受常染色体上一对等位基因控制,与果蝇眼形相关的基因型有____ 种;若这对基因位于性染色体(X、Y染色体上的I区段),则与果蝇眼形相关的基因型有____ 种.

(3)若F2中圆眼:棒眼=3:1,且仅雄果蝇中有棒眼,则控制圆眼、棒眼的等位基位于性染色体上,可能位于乙图中X、Y染色体的____ 区段.

(4)若已经研究清楚,该对性状受常染色体上一对等位基因控制.圆眼纯合果蝇与棒眼果蝇杂交,在后代群体中出现了一只棒眼果蝇.出现该棒眼果蝇的原因可能是亲本果蝇在产生配子过程中发生了基因突变或染色体片段缺失,为了探究其原因,现有人设计了如下的实验步骤,请您帮助完成结果预测.(注:一对同源染色体都缺失相同片段时胚胎致死;各型配子活力相同)

①用该棒眼果蝇与基因型为Aa的果蝇杂交,获得F1;

②F1自由交配,观察、统计F2表现型及比例.

结果预测:

Ⅰ.如果F2表现型及比例为圆眼:棒眼=____ ,则为基因突变;

Ⅱ.如果F2表现型及比例为圆眼:棒眼=____ ,则为染色体片段缺失.

同类题3

根据短文理解,选择正确答案。

7 January, 2014

    A new report says more and more international students are attending colleges and universities in the United States. It also notes a large increase in the number of international students from China.

    These findings are from the latest Open Doors Report. The report documents the record number of international students in the United States during 2012, 2013 school year. It says more than seven hundred sixty-four thousand four-hundred such students were attending American colleges and universities during the last two years. That represents an increase of almost six percent than one year earlier. On the other hand, the number of Americans studying overseas(海外) increased by one percent, which reached nineteen thousand this year.

    The report says one hundred ninety-four thousand students at American colleges and universities were from China .That is an increase of more than twenty-three percent over the year before. Peggy Blumenthal, an expert(专家)of international education, described the effect of the increase in Chinesestudents.

    "Now they have been coming for some time. But this year was the highest level ever." She says many Chinese families are able to pay for the highest-quality education for their children. The children mainly choose to study in America.

    "We know many of them have enough income to be able to afford to send them anywhere in the world if they want to go. And for the most part, looking around the world, Chinese students still prefer to come to the United States as their choice."

    Chinese students are not the only ones who want to attend American colleges and universities. After China, India sends the second largest number of students to the United States for higher education. India has about one hundred thousand students in American schools. South Korea is third with about seventy-two thousand students.

    Why do so many foreign students study in the United States? Peggy Blumenthal provides one reason.

    "The advantage America has is that we have a huge system (系统)and a very perfect system. So there are over four thousand universities and colleges in the United States. Among them are some top ones in the world, and what that tells us is there is still a lot of room to host international students.

    Foreign students represent less than four percent of the total student population in American higher education. And from Learning English, that's the VOA Special English Education Report. I'm Bob Doughty. Thanks for listening.