雅思閱讀練習題
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Smoking leaves an "archaeological record" of the hundreds of DNA mutations it causes, scientists have discovered.
Having sequenced thousands of tumour genomes, they found a 20-a-day smoker would rack up an average of 150 mutations in every lung cell each year.
The changes are permanent, and persist even if someone gives up smoking.
Researchers say analysing tumour DNA may help explain the underlying causes of other cancers.
Pamela Pugh, 69, was diagnosed with lung cancer in 2013. She started smoking aged 17 and quit in her early 50s.
But she said: "Even though I gave up many years ago, the effects of smoking caught up with me.
"Had I known as a teenager that smoking caused mutations which would stay with me for life then I would never had started".
The study, in the journal Science, was carried out by an international group, including the Wellcome Trust Sanger Institute in Cambridgeshire and the Los Alamos National Laboratory in New Mexico.
The analysis shows a direct link between the number of cigarettes smoked in a lifetime and the number of mutations in tumour DNA.
The authors found that, on average, smoking a packet of cigarettes a day led to:
150 mutations in each lung cell every year
97 in the larynx or voice box
23 in the mouth
18 in the bladder
six in the liver
Joint lead author Prof Sir Mike Stratton, from the Wellcome Trust Sanger Institute, said: "The more mutations there are, the higher the chance that these will occur in the key genes that we call cancer genes, which convert a normal cell into a cancer cell."
There are 35,000 deaths a year in the UK from lung cancer, and it is estimated that nine out of 10 cases are preventable.
科學家研究發現，吸煙會導致DNA突變，給人留下數百種基因突變的“永久記錄”。
在對數千個腫瘤基因組進行測序后，科學家發現每天吸煙20支的人每年每個肺細胞累積平均有150個基因突變。
這些突變是永久且持續的，即使吸煙者戒煙也不可逆。
研究人員說，分析腫瘤DNA能幫助解釋其他癌癥的深層原因。
69歲的帕梅拉-皮尤2013年被診斷患有肺癌。她自17歲開始吸煙，近50歲時戒煙。
但她說：“盡管我很多年前就戒煙了，但吸煙的影響一直在。”
“如果年輕時我知道吸煙導致的基因突變一生都會跟隨著我，那么我絕不會開始吸煙。”
這項研究發表在《科學》期刊上，由一個國際研究組研究得出，包括英國劍橋郡的基金會桑格研究院，以及美國新墨西哥州的洛斯阿拉莫斯國家實驗室。
研究顯示，人一生中吸煙的總數量和腫瘤DNA變異的.數量之間存在直接關系。
研究作者發現，平均來講，每天吸一包煙會導致：
每年每個肺部細胞中有150個基因突變。
喉部或喉頭97個突變
口腔部位23個突變
膀胱18個突變
肝臟6個突變
研究報告的合作主創者、來自基金會桑格研究院的邁克-斯特拉頓教授說：“突變越多，關鍵基因，也就是我們所說的癌癥基因發生突變的幾率也就越大，這會將正常細胞轉變為癌細胞。”
英國每年有3.5萬人死于癌癥，據估計其中九成可以預防。
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