问题 问答题 简答题

何谓转化?试述转化的具体过程。

答案

参考答案:

转化:受体菌直接吸收外源DNA片段,通过交换把它整合到自己的基因组中,再经复制就使自己变成一个转化子,这种受体菌接受外源DNA片段而获得部分新遗传性状的现象称为转化。

具体过程:转化因子与感受态细胞结合:双链DNA片段与感受态受体菌细胞表面特定位点相结合。转化DNA被酶解:吸附位点上的DNA被核酸内切酶分解成适当大小DNA片段。单链DNA进入宿主细胞:外源DNA片段与受体细胞核染色体组发生同源配对、交换、取代,形成杂合DNA区段。染色体DNA复制、分离:受体菌染色体组进行复制与分离。形成转化子:细胞分裂后,一个子细胞为转化子,另一个子细胞为非转化子。

单项选择题
单项选择题

Are teens and young adults more narcissistic (自恋的) today than in the past That’s the view of a California researcher who studies (1) people.

In her new book, The Narcissism (2) : Living in the Age of Entitlement, psychologist Jean Twenge of San Diego State University and (3) W. Keith Campbell of the University of Georgia say research shows (4) young people today have "narcissistic traits" than in (5) generations. Such traits, Twenge says, include a very. (6) and inflated sense of self, which is (7) by a preoccupation with MySpace, Facebook and YouTube.

"We’ve been on this self-admiration cultural (8) for a long time," Twenge says. (9) Twenge’s take on today’s young people isn’t universal. Studies by other researchers, including Canadian (10) Dr. Kali of the University of Western Ontario, have used the same data but found (11) results. "They put a different (12) on it," Kali says.

Twenge’s studies have found more narcissistic traits and a (13) rate of increase among college students today, but Kali found that students’ narcissism was (14) greater in 2006 than in 1976. Twenge’s most recent paper studied the same data as Kali--more than 20 000 college students from 2002 to 2007. (15) researchers used the Narcissistic Personality Inventory to measure narcissistic (16) and findings by both have been (17) in peerreviewed journals.

Twenge’s book (18) just a month after The Mirror Effect : How Celebrity Narcissism Is Seducing America, a book co-written by behavioral (19) Drew Pinsky, (20) suggested that a celebrity-obsessed culture is causing more narcissism.

17()

A.rejected

B.reported

C.accepted

D.published