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  Research using twins

  To biomedical researchers all over the world, twins offer a precious opportunity to untangle the influence of genes and the environment — of nature and nurture. Because identical twins come from a single fertilized egg that splits into two, they share virtually the same genetic code. Any differences between them — one twin having younger looking skin, for example — must be due to environmental factors such as less time spent in the sun.

  Alternatively, by comparing the experiences of identical twins with those of fraternal twins, who come from separate eggs and share on average half their DNA, researchers can quantify the extent to which our genes affect our lives. If identical twins are more similar to each other with respect to an ailment than fraternal twins are, then vulnerability to the disease must be rooted at least in part in heredity.

  These two lines of research — studying the differences between identical twins to pinpoint the influence of environment, and comparing identical twins with fraternal ones to measure the role of inheritance — have been crucial to understanding the interplay of nature and nurture in determining our personalities, behavior, and vulnerability to disease.

  The idea of using twins to measure the influence of heredity dates back to 1875, when the English scientist Francis Galton first suggested the approach (and coined the phrase ‘nature and nurture’). But twin studies took a surprising twist in the 1980s, with the arrival of studies into identical twins who had been separated at birth and reunited as adults. Over two decades 137 sets of twins eventually visited Thomas Bouchard’s lab in what became known as the Minnesota Study of Twins Reared Apart. Numerous tests were carried out on the twins, and they were each asked more than 15,000 questions.

  Bouchard and his colleagues used this mountain of data to identify how far twins were affected by their genetic makeup. The key to their approach was a statistical concept called heritability. In broad terms, the heritability of a trait measures the extent to which differences among members of a population can be explained by differences in their genetics. And wherever Bouchard and other scientists looked, it seemed, they found the invisible hand of genetic influence helping to shape our lives.

  Lately, however, twin studies have helped lead scientists to a radical new conclusion: that nature and nurture are not the only elemental forces at work. According to a recent field called epigenetics, there is a third factor also in play, one that in some cases serves as a bridge between the environment and our genes, and in others operates on its own to shape who we are.

  Epigenetic processes are chemical reactions tied to neither nature nor nurture but representing what researchers have called a ‘third component’. These reactions influence how our genetic code is expressed: how each gene is strengthened or weakened, even turned on or off, to build our bones, brains and all the other parts of our bodies.

  If you think of our DNA as an immense piano keyboard and our genes as the keys — each key symbolizing a segment of DNA responsible for a particular note, or trait, and all the keys combining to make us who we are — then epigenetic processes determine when and how each key can be struck, changing the tune being played.

  One way the study of epigenetics is revolutionizing our understanding of biology is by revealing a mechanism by which the environment directly impacts on genes. Studies of animals, for example, have shown that when a rat experiences stress during pregnancy, it can cause epigenetic changes in a fetus that lead to behavioral problems as the rodent grows up. Other epigenetic processes appear to occur randomly, while others are normal, such as those that guide embryonic cells as they become heart, brain, or liver cells, for example.

  Geneticist Danielle Reed has worked with many twins over the years and thought deeply about what twin studies have taught us. ‘It’s very clear when you look at twins that much of what they share is hardwired,’ she says. ‘Many things about them are absolutely the same and unalterable. But it’s also clear, when you get to know them, that other things about them are different. Epigenetics is the origin of a lot of those differences, in my view.’

  Reed credits Thomas Bouchard’s work for today’s surge in twin studies. ‘He was the trailblazer,’ she says. ‘We forget that 50 years ago things like heart disease were thought to be caused entirely by lifestyle. Schizophrenia was thought to be due to poor mothering. Twin studies have allowed us to be more reflective about what people are actually born with and what’s caused by experience.’

  Having said that, Reed adds, the latest work in epigenetics promises to take our understanding even further. ‘What I like to say is that nature writes some things in pencil and some things in pen,’ she says. Things written in pen you can’t change. That’s DNA. But things written in pencil you can. That’s epigenetics. Now that we’re actually able to look at the DNA and see where the pencil writings are, it’s sort of a whole new world.’

  Questions 1-4

  Do the following statements agree with the information given in Reading Passage 1?

  In boxes 1-4 on your answer sheet, write


  TRUE if the statement agrees with the information

  FALSE if the statement contradicts the information

  NOT GIVEN if there is no information on this

  1 There may be genetic causes for the differences in how young the skin of identical twins looks.

  2 Twins are at greater risk of developing certain illnesses than non-twins.

  3 Bouchard advertised in newspapers for twins who had been separated at birth.

  4 Epigenetic processes are different from both genetic and environmental processes.

  Questions 5-9

  Look at the following statements (Questions 5-9) and the list of researchers below.

  Match each statement with the correct researcher, A, B or C.

  Write the correct letter, A, B or C, in boxes 5-9 on your answer sheet.

  NB You may use any letter more than once.

  List of Researchers

  A Francis Galton

  B Thomas Bouchard

  C Danielle Reed

  5 invented a term used to distinguish two factors affecting human characteristics

  6 expressed the view that the study of epigenetics will increase our knowledge

  7 developed a mathematical method of measuring genetic influences

  8 pioneered research into genetics using twins

  9 carried out research into twins who had lived apart

  Questions 10-13

  Complete the summary using the list of words, A-F, below.

  Write the correct letter, A-F, in boxes 10-13 on your answer sheet.

  Epigenetic processes

  In epigenetic processes, 10 __________ influence the activity of our genes, for example in creating our internal 11 __________ The study of epigenetic processes is uncovering a way in which our genes can be affected by our 12 __________ One example is that if a pregnant rat suffers stress, the new-born rat may later show problems in its 13 __________.

  A nurture B organs C code

  D chemicals E environment F behaviour/behavior


  Passage 1

  Question 1

  答案: FALSE

  关键词: genetic causes, skin

  定位原文: 第1段第2、3句“Because identical twins come from…”同卵双胞胎享有同样的基因密码,两人出现不同只可能是环境因素造成的差异。

  解题思路: 本题出题位置符合顺序原则,作为文后第一个题型中的第一道题,考生可以轻松在正文第一段中定位到一模一样的skin一词。从理解上来看本题也并不困难:原文明确说到同卵双胞胎来自同一颗受精卵,基因完全相同,一切不同都是后天环境因素造成的。这与题干信息“同卵双胞胎的皮肤看起来有多年轻,其背后有可能存在着基因方面的原因”相悖,因此答案为FALSE。

  Question 2


  关键词: greater risk, developing certain illnesses, non-twins

  定位原文: 第2段第2句“If identical twins are…”

  解题思路: 题干中的illness 一词回到原文中有两个对应的同义替换词,分别为ailment 和disease。即使对前者不甚熟悉但必定应当认识后者,所以定位并不算难。仔细阅读文章内容可知,本句只是提及同卵双胞胎与异卵双胞胎在对某种疾病产生反应的方面有何异同,比较的对象只涉及“双胞胎”这个范围,并未将之与“非双胞胎”比较,没有明确提及题干的信息“双胞胎比非双胞胎更有风险得上某些疾病”,通读后文后,也没有其他的答题定位区域,因此答案为NOT GIVEN。

  Question 3


  关键词: Bouchard, advertised, newspapers

  定位原文: 第4段第2句“Over two decades 137 sets of …”

  解题思路: 本题可以凭借Bouchard这个专有名词而轻松在文中定位,但仔细阅读文章内容就会发现,确实有许多双胞胎参与了此人所进行的研究,但并没有明确提及那些双胞胎们是通过什么途径来到Bouchard实验室的,没有“报纸”和“广告”这些信息,因此答案是NOT GIVEN。

  Question 4

  答案: TRUE

  关键词: epigenetic processes

  对应原文: 第6段最后一句“According to a recent field called …”

  解题思路: Epigenetic这个词作为学科名称,一模一样地出现在文中第6段,可以被轻松定位。阅读定位句则可以知道,这一作用过程确实既不同于环境因素,也不同于基因因素,与题干表述相一致,因此答案为TRUE。

  Question 5

  答案: A

  关键词: invented a term, two factors

  定位原文: 第4段第1句“The idea of using twins…”

  解题思路: 题目:invented a term used to distinguish two factors affecting human characteristics; 译文:发明了一个术语用来区分影响个人特质的两种因素。本题基本上就是考査考生对coin这个单词作为动词表示“创造”;这个单词作为名词还可表示“术语——这个词汇知识点,而coin a term这样的用法在此前的剑桥真题里已经出现过,此题答案为A。

  Question 6

  答案: C

  关键词: study of epigenetics, increase, knowledge

  定位原文: 第12段最后1句“Having said that, Reed … ”

  解题思路: 题目:expressed the view that the study of epigenetics will increase our knowledge;译文:表达了这样一个观点:对于表观遗传学的研究将会增加我们的知识。本题的定位稍有麻烦,因为Reed这个人名在文章的后三段中都有所提及,对比这几段文章中的相关内容,待读到最后一段时理解原文应该不难,increase our knowledge 与 take our understanding further 是简单的同义表述关系,本题答案为C。

  Question 7

  答案: B

  关键词: mathematical method

  定位原文: 第5段第1、2句“Bouchard and his colleagues …”

  解题思路: 题目:developed a mathematical method of measuring genetic influences;译文:开创了一种数学方法来衡量基因的影响。本题出题点距离人名定位处并不远,statistical concept 与 mathematical method 为同义替换关系,此题答案为B。

  Question 8

  答案: A

  关键词: pioneered

  定位原文: 第4段第1句“The idea of using twins to measure…”

  解题思路: 题目:pioneered research into genetics using twins; 译文:开创了通过双胞胎来研究基因学的做法。本题与第五题的定位完全相同,都是原文中的同一句,且从考查单词的难度上来看,比第5题更容易理解。无论date back (追溯到)这个词组还是first这个单词都不会造成理解困难,正是Francis Galton开创了研究双胞胎的先河,本题答案为A。

  Question 9

  答案: B

  关键词: lived apart

  定位原文: 第4段第2、3句“But twin studies took a surprising twist in…”

  解题思路: 题目:carried out research into twins who had lived apart; 译文:对那些各自生活在不同地方的双胞胎进行了研究。无论是原文中第二句里的separated at birth and reunited as adults 还是第三句里的 Reared apart, 都明确对应题干中的lived apart这个信息,只需明确这个研究对象到底是Francis Galton还是Thomas Bouchard所研究的即可。经过仔细阅读可知为后者,因此本题答案为B。

  Question 10

  答案: D

  关键词: epigenetic processes

  定位原文: 第7段第1、2句“Epigenetic processes…”

  解题思路: 题干说“在表观遗传过程中,_____会影响我们的基因活动行为”。用epigenetic processes可以轻松在原文中定位到出题位置,但需要耐心读完相邻的两句,才可根据后句里的these reactions这个指代更加确定答案应为前一句中的chemical reactions, 根据意思选择最接近的选项,由此可得答案为D。

  Question 11

  答案: B

  关键词: create, internal

  定位原文: 第7段第2句“These reactions …”

  解题思路: 题干说“在表观遗传过程中,化学反应会影响我们的基因活动行为,例如在创造我们内部_____的时候”。本题的出题位置与上一题来自同一句话,看出原文中的 parts of our bodies 正是对应 internal organs 这一表述,因此答案为B选项:organs。

  Question 12

  答案: E

  关键词: uncover, genes, affected

  定位原文: 第9段第1句“One way the study of …”

  解题思路: 题干说“表观遗传学的研究正在探索我们的基因会以怎样的方式受到我们的_____的影响”。考生应该不难找到原文中impact与题干中be affected by的同义替换,对比可知答案为E选项:environment。

  Question 13

  答案: behaviour/behavior

  关键词: pregnant rat, stress, problems

  定位原文: 第9段第2句“Studies of animals, for example, have shown…”

  解题思路: 题干说“有一个例证:如果一只怀孕的老鼠经历过紧张压力体验,新生的幼鼠日后就有可能展现出_______方面的问题”。“怀孕的老鼠”这个信息在文中容易定位,考生只需认真阅读定位句即可得出答案为F选项。

  雅思阅读部分的备考,需要多加练习,以上智课网为大家分享的雅思阅读考前练习:Research using twins,就是一个很好的练习机会。