题干

家蚕的性别决定为ZW型。用X射线处理使第2染色体上的含显性斑纹基因PB的区段易位到W染色体上,再将雌蚕与白体雄蚕交配,其后代凡是雌蚕都有斑纹,凡是雄蚕都无斑纹,这样有利于“去雌留雄”,提高蚕丝产量。该育种方法依据的原理是

A:基因突变

B:基因重组

C:染色体结构的变异 

D:染色体数目的变异

上一题 下一题 0.0难度 选择题 更新时间:2019-04-20 08:07:09

答案(点此获取答案解析)

C

同类题5

阅读下列短文,从每题所给的四个选项(A、B、C和D)中,选出最佳选项。

    Surfing the Internet for fun will make you a better employee, according to an Australian study.

    The University of Melbourne study shows that people who use the Internet for their own reasons at work are about 9 percent more productive(具有创造性的) than those who do not. Study author Brent Coker said, “Surfing the Internet at times helps increase workers' attention.”

    “People need to relax for a bit to get back their attention,” Coker said on the university's website. “Having a short break, such as a quick surfing of the Internet, helps the mind to rest itself, leading to a higher total Internet attention for a day's work, and as a result, increases productivity (生产效率),” he said.

    According to the study of 300 workers, 70 percent of people who use the Internet at work surf the Internet for their own reasons during office hours. Among the most popular surfing activities are searching for information about products, reading online news, playing online games and watching videos. “Firms spend a lot of money on software to block their workers from watching videos, using social networking sites or shopping online,” said Coker. “That's not always a good idea.”

    However, Coker said the study looked at people who surfed the Internet in moderation(适度), or were on the Internet for less than 20 percent of their total time in the office. “Those who spend too much time surfing the Internet will have a lower productivity than those without.” he said.