问题 问答题

F+菌株与Hfr菌株有何异同点

答案

参考答案:两菌株的共同点:①他们都具有F因子,细胞的表面有性伞毛,F-细胞表面没有这种突起;②两种菌株都能与F-菌株杂交。
两菌株的不同点:①F因子在细菌细胞中存在的状态不同,F+菌株中的F因子独立于细菌染色体之外,而Hfr菌株中的F因子整合在细菌染色体内,同细菌染色体一起复制和遗传。②与F-菌株杂交的结果不同,在F+与F-杂交时,F因子通过滚环复制转移到F-细胞中,使F-细胞转变为F+细胞,但原F+细胞中细菌的染色体或基因很少转移给F-细胞;当Hfr与F-细胞杂交时,两细菌的重组率相当高,但很少能使F-细胞转变为F+细胞。

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8:30 PM

Outlook

Outlook is back with a new series of reports to keep you up date with all that’s new in the world of entertainment. Stories go all the way from the technical to the romantic, from stage to screen. There will be reports of the stars of the moment, the stars of the future and the stars of the past. The director with his new film,he designer with the latest fashion and the musician with the popular song are part of the new Outlook . The program is introduced by Fran Levine.

9:00 PM

Discovery

When a 10-year-old boy gets a first class degree in mathematics or an 8-year-old plays chess like a future grand master, they are considered as geniuses . Where does the quality of genius come from? Is it all in the genes (基因) or can any child be turned into a genius ? And if parents do have a child who might become a genius in the future,what should they do? In this 30-minute film, Barry Johnson , the professor at School of Medicine , New York University will help you discover the answer .

10:00 P

Science/Health

Is it possible to beat high blood pressure without drugs? The answer is “yes”, according to the researchers at Johns Hopkins  and three other medical centers . After a study of 800 persons with high blood pressure , they found that after 6 months , those devoted to weight loss—exercise and eating a low—salt , low-fat food—lost about 13 pounds and became fitter . Plus , 35% of them dropped into the “normal” category(范畴). This week, Dr . Alan Duckworth will tell you how these people reduce their blood pressure to a level similar to what’s achieved with Hypertension drugs .

小题1:The main purpose of writing these three texts is        .

A.to invite people to see films

B.to invite people to topic discussions

C.to attract more students to attend lectures

D.to attract more people to watch TV programs小题2:From Outlook , you can get a great deal of information about          .

A.story tellers

B.famous stars

C.film companies

D.music fans小题3:Who will be most probably interested in Discovery ?

A.Parents who want to send their children to a school of medicine .

B.Children who are good at mathematics .

C.Parents who want their child to become another Albert Einstein .

D.Children who are interested in playing chess .小题4:In Science / Health; “Johns Hopkins” is             .

A.a famous university

B.a medical center

C.a well-known doctor

D.a drug company小题5:According to the third text , which of the following has almost the same effect as Hypertension drug ?

A.Exercise plus a healthy diet .

B.Loss of thirteen pounds in weight .

C.Six months of exercise without drugs .

D.Low-salt and low-fat food .