问题 单项选择题

关于遗传信息及其传递过程,下列叙述正确的是()。

A.遗传信息只能储存于细胞核,通过复制传递给下一代

B.同一细胞在不同时期的转录产物可以不同

C.转录和翻译时的模板及碱基互补配对方式都相同

D.真核细胞与原核细胞共用一套密码子.说明真核生物由原核生物进化而来

答案

参考答案:B

解析:原核生物的遗传信息在拟核不在细胞核.A错误。同一细胞因为在不同时期基因的选择性表达,转录产物可能不同,如红细胞,B正确。转录时碱基互补配对有T-A,但翻译时只有U-A,C错误。真核细胞与原核细胞共有一套密码子,说明生物有共同的祖先,D错误。

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I am honored to be here today, (1) Harvard at this celebration of the College Board’s half century of working to promote (2) and equal opportunity in higher education.
Before I say anything else, I want to thank everyone in the room for the work you do every day to make college (3) , available, and (4) for millions of young people across the country.
I want to focus my remarks on a matter of (5) to American familiesand to the future of the nation -- restoring education to its proper role as a (6) to equal opportunity and (7) in our society.
This has been an (8) in higher education, with great and creative efforts made by many institutions. Earlier this year, we announced a new (9) at Harvard aimed at the students from families of low and (10) income. Under our new program, families with incomes of (11) will no longer be expected to contribute to the cost of attending Harvard for their children. Families with incomes of less than $ 60,000 will also see their (12) reduced.
We are proud of this effort at Harvard, but we are aware that the programs of individual institutions with means can never be a substitute for our shared (13) to provide adequate funding for Pell grants and other financial aid, and for the state and community college systems that make higher education (14) and affordable for the (15) .
There is something empty about (16) initiatives that may be right for one institution without attention to their broader impact. (17) , we (18) if we urge changes in national policy without doing what we can on our own campuses.
In this spirit, I want to (19) today a problem that is emerging with (20) in this nation.

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