exam-epigenetics

1、2008 年《表觀遺傳學(xué)》期末測試卷 年《表觀遺傳學(xué)》期末測試卷姓名： 學(xué)號：*********************************************************************答題要求 答題要求：1. 考試方式采取課后完成的方式，學(xué)生可參考課件、參考教材及其他相關(guān)資料；2. 試卷不需打印，統(tǒng)一采用電子版答題，試卷答題完畢，請將答題完畢的本文

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3、5. 請不要直接拷貝網(wǎng)上現(xiàn)成的資料，凡 google 搜索 6 字相同，亦將被認(rèn)定為作弊嫌疑；6. 答題建議使用中文，若采用英文答題，需注意英文的單復(fù)數(shù)、語法等，有誤將加扣英文語法分；不易翻譯的名詞可用英文；字體格式為：宋體，小四 *********************************************************************一、癌癥細(xì)胞與正常細(xì)胞中的表觀遺傳特征有何不同，請至少舉出兩個(gè)例子。二

4、、舉例說明基因組印記是如何實(shí)現(xiàn)僅表達(dá)一個(gè)等位基因座的分子機(jī)制。三、DNA 甲基化是如何抑制基因轉(zhuǎn)錄的？請至少給出兩種可能的分子機(jī)制。DNA methylation patterns across the X chromosome. Active and inactive copies were distinguished by gene-expression and DNA-replication analyses, and DNA

5、methylation patterns were compared in clonal cell lines, derived from a given individual, that had inactivated either the maternal or the paternal copy of the X chromosome.The results showed a strikingly higher level o

6、f allele-specific DNA methylation on the Xa than on its inactive counterpart, at a ratio of about 2.4:1. Most of this methylation occurs within the bodies of genes (the transcribed regions), rather than in upstream prom

7、oters or intergenic areas. The authors found no biases that give a clue to the function of this methylation; for example, methylation was not especially common at tissue-specific genes or repetitive elements.Does this r

8、elative hypermethylation on the Xa result from active methylation on this copy, or from demethylation of the Xi? To answer this question, Hellman and Chess looked at a human embryonic stem cell line, which is presumed to

9、 represent a stage in development before X inactivation. Few of the Xa-specific methylation sites were methylated monoallelically in these cells, indicating that biallelic methylation is the initial state, with later de

10、methylation of the Xi at gene bodies.The authors suggest a model for this differential DNA methylation pattern on the two copies of the X chromosome. They propose that inactive, untranscribed regions, such as the Xi and

11、intergenic regions, are more likely to undergo loss of methylation, resulting in higher methylation levels remaining at gene bodies on the Xa. Whether this is the case or not, this study alters our views of DNA methylat

12、ion on the X chromosome, revealing marked differences outside the promoter regions that have been the focus of previous studies and setting the scene for other reassessments of DNA methylation patterns.ORIGINAL RESEARCH