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  3. Researchers have known for years that children whose mothers were chronically stressed during pregnancy—by famine, anxiety, the

Researchers have known for years that children whose mothers were chronically stressed during pregnancy—by famine, anxiety, the

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问题    Researchers have known for years that children whose mothers were chronically stressed during pregnancy—by famine, anxiety, the death of a relative or marital discord, for instance—show higher-than-normal rates of various psychological and behavioural disorders when they are adults. They have also known for a long time that those brought up in abusive environments often turn out to be abusive themselves. The second of these observations is usually put down to learning. The reason for the first has remained unclear. A study just published by Axel Meyer, Thomas Elbert and their colleagues at the University of Konstanz in Germany, however, points to a phenomenon called epigenetics as the likely answer. Epigenetics is a type of gene regulation that can be passed from a cell to its daughters. The most common mechanism is methylation, whose consequence is to inactivate the gene being methylated.
   They found that women abused during pregnancy were significantly more likely than others to have a child with methylated glucocorticoid-receptor genes. By contrast, abuse before or after pregnancy resulted in no such correlation. Nor was the mother’s own methylation affected by violence towards her. Taken together, these results suggest that glucocorticoid-receptor-gene methylation happens in the fetus in response to a mother’s stress, and persists into adolescence.
   This has implications for those adolescents’ long-term health. Dampened glucocorticoid-receptor-gene activity has been shown to increase the risk of obesity and of depression. It also makes people more impulsive and aggressive—and therefore, if male, more likely to abuse the pregnant mothers of their children, thus perpetuating the whole sorry cycle.
   Why, in light of such negative effects, have humans evolved to be programmed this way while still in the womb? Part of the answer is probably that not all the negative consequences would have shown up at the time the mechanism was evolving. The other part is that some of the consequences probably have a positive effect.
   What can be done with such knowledge is unclear. Drugs that demethylate DNA are under development, but are still some way from approval—and, in any case, interfering with epigenetics, which is a widespread mechanism of gene regulation, is a drastic approach. The research might, though, point to the period when intervening to stop abuse will have the greatest effect. Then again, such intervention is always desirable, for the sake of both mother and child.
   
Which might be the appropriate title of this passage?
选项 A、Genes and Methylation
B、Epigenetics and Stress
C、Inheritance of Abusiveness
D、Intervention of Methylation
答案B
解析 主旨题。根据题干关键词需纵观全文，但文章第一段段末就指出了关键词epigenetics(外因遗传)，同时第一段描述的孕妇的种种处境，都是在强调其孕期所承受的压力，故B项“外因遗传与压力”为正确答案。
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